विभाग:Convert

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This module converts a value from one unit of measurement to another. For example:

  • {{convert|123|lb|kg}} → 123 pounds (56 kg)

The module is called using a template—parameters passed to the template are used by this module to control how a conversion is performed. For example, units can be abbreviated (like kg), or displayed as names (like kilogram), and the output value can be rounded to a specified precision. For usage information, see Help:Convert.

The template that invokes this module is:

The following modules are required:

The following modules are optional and are used only if required and if the module exists:

The following help pages are available:

A page containing a convert error is added to the following hidden category, providing the page is in a specified namespace (articles, by default):

Units are defined in the wikitext of the master list of units.

Module:Convert/data is transcluded into every page using the convert module, so experimenting with a new unit in that module would involve a significant overhead. The Module:Convert/extra module is an alternative which is only transcluded on pages with a unit that is not defined in the main data module.


Sandbox

When making a change, copy the current modules to the sandbox pages, then edit the sandbox copies:

Use the following template to test the results (example {{convert/sandbox|123|lb|kg}}):

Template:Convert/sandbox invokes Module:Convert/sandbox with parameter |sandbox=sandbox which causes convert to use the sandbox modules rather than the normal modules.

The following should be used to test the results of editing the convert modules.

It is not necessary to save a testcases page before viewing test results. For example, Template:Convert/testcases/sandbox4 could be edited to change the tests. While still editing that page, paste "Template talk:Convert/testcases/sandbox4" (without quotes) into the page title box under "Preview page with this template", then click "Show preview".

Configuration

The template that invokes this module can define options to configure the module. For example:

  • {{#invoke:convert|convert|numdot=,|numsep=.}}
Sets the decimal mark to be a comma, and the thousands separator to be a dot.

Other options, with default values, are:

  • |maxsigfig=14 – maximum number of significant figures
  • |nscat=0namespaces (comma separated) in which an error or warning adds a category to the page
  • |warnings=0 – 0 (zero) disables warnings; 1 shows important warnings; 2 shows all warnings

An option in the template can specify that the sandbox versions of the modules be used. If specified, the text on the right-hand side of the equals sign must be the name of the subpage for each sandbox module.

  • |sandbox=sandbox – omit for normal operation

All text used for input parameters and for output messages and categories can be customized. For example, at enwiki the option |lk=on can be used to link each displayed unit to its article. The "lk" and "on" can be replaced with any desired text. In addition, input and output numbers can be formatted and can use digits in the local language. See the translation guide for more information.

To do

Document the modules to access Wikidata! Error

Could not read wikitext from "Module:Convert/data/sandbox".


-- Convert a value from one unit of measurement to another.
-- Example: {{convert|123|lb|kg}} --> 123 pounds (56 kg)

local MINUS = '−'  -- Unicode U+2212 MINUS SIGN (UTF-8: e2 88 92)
local abs = math.abs
local floor = math.floor
local format = string.format
local log10 = math.log10
local ustring = mw.ustring
local ulen = ustring.len

-- mw.ustring has two bugs: following works around one of them; see "2013-07-05" for second.
-- Bug has been reported, and the fix will be deployed, possibly before August 2013.
-- local usub = ustring.sub
-- When fix is deployed, remove following usub function, and uncomment above usub variable.
local function usub(s, i, j)
    return (j and i > j) and '' or ustring.sub(s, i, j)
end

-- Configuration options to keep magic values in one location.
-- The conversion data and message text are defined in separate modules.
local numdot, numsep  -- each must be a single byte for simple regex search/replace
local maxsigfig, warnings
local default_exceptions, link_exceptions, all_units
local SIprefixes, all_categories, all_messages, customary_units, disp_joins
local en_option_name, en_option_value, eng_scales, range_aliases, range_types
local group_method = 3     -- code for how many digits are in a group
local plural_suffix = 's'  -- only other useful value is probably '' to disable plural unit names
local from_en_table  -- to translate an output string of en digits to local language
local to_en_table    -- to translate an input string of digits in local language to en

-- All units should be defined in the data module. However, to cater for quick changes
-- and experiments, any unknown unit is looked up in an extra data module, if it exists.
-- That module would be transcluded in only a small number of pages, so there should be
-- little server overhead from making changes, and changes should propagate quickly.
local extra_module  -- name of module with extra units
local extra_units   -- nil or table of extra units from extra_module

local function boolean(text)
    -- Return true if text represents a "true" option value.
    if text then
        text = text:lower()
        if text == '1' or text == 'y' or text == 'yes' or text == 'on' or text == 'true' then
            return true
        end
    end
end

local function from_en(text)
    -- Input is a string representing a number in en digits with '.' decimal mark,
    -- without digit grouping (which is done just after calling this).
    -- Return the translation of the string with numdot and digits in local language.
    if numdot ~= '.' then
        text = text:gsub('%.', numdot)
    end
    if from_en_table then
        text = text:gsub('%d', from_en_table)
    end
    return text
end

local function to_en(text)
    -- Input is a string representing a number in the local language with
    -- an optional numdot decimal mark and numsep digit grouping.
    -- Return the translation of the string with '.' mark and en digits,
    -- and no separators (they have to be removed here to handle cases like
    -- numsep = '.' and numdot = ',' with input "1.234.567,8").
    if numsep ~= '' then
        text = text:gsub('[' .. numsep .. ']', '')  -- use '[x]' in case x is '.'
    end
    if numdot ~= '.' then
        text = text:gsub('[' .. numdot .. ']', '.')
    end
    if to_en_table then
        text = ustring.gsub(text, '%d', to_en_table)
    end
    return text
end

local spell_module  -- name of module that can spell numbers
local speller       -- function from that module to handle spelling (set if spelling is wanted)

local function set_config(frame)
    -- Set configuration options from template #invoke or defaults.
    local args = frame.args
    numdot = args.numdot or '.'       -- decimal mark before fractional digits
    numsep = args.numsep or ','       -- group separator for numbers (',', '.', '')
    maxsigfig = args.maxsigfig or 14  -- maximum number of significant figures
    warnings = boolean(args.warnings) -- true if want warnings for invalid options
    -- Scribunto sets the global variable 'mw'.
    -- A testing program can set the global variable 'is_test_run'.
    local data_module, text_module, data_code, text_code
    if is_test_run then
        local langcode = mw.language.getContentLanguage().code
        data_module = "convertdata-" .. langcode
        text_module = "converttext-" .. langcode
        extra_module = "convertextra"
        spell_module = "ConvertNumeric"
    else
        data_module = "Module:Convert/data"
        text_module = "Module:Convert/text"
        extra_module = "Module:Convert/extra"
        spell_module = "Module:ConvertNumeric"
    end
    data_code = mw.loadData(data_module)
    text_code = mw.loadData(text_module)
    default_exceptions = data_code.default_exceptions
    link_exceptions = data_code.link_exceptions
    all_units = data_code.all_units
    SIprefixes = text_code.SIprefixes
    all_categories = text_code.all_categories
    all_messages = text_code.all_messages
    customary_units = text_code.customary_units
    disp_joins = text_code.disp_joins
    en_option_name = text_code.en_option_name
    en_option_value = text_code.en_option_value
    eng_scales = text_code.eng_scales
    range_aliases = text_code.range_aliases
    range_types = text_code.range_types
    local translation = text_code.translation_table
    if translation then
        if translation.group then
            group_method = translation.group
        end
        if translation.plural_suffix then
            plural_suffix = translation.plural_suffix
        end
        from_en_table = translation.from_en
        local use_workaround = true
        if use_workaround then
            -- 2013-07-05 workaround bug by making a copy of the required table.
            -- mw.ustring.gsub fails with a table (to_en_table) as the replacement,
            -- if the table is accessed via mw.loadData.
            local source = translation.to_en
            if source then
                to_en_table = {}
                for k, v in pairs(source) do
                    to_en_table[k] = v
                end
            end
        else
            to_en_table = translation.to_en
        end
    end
end

local function collection()
    -- Return a table to hold items.
    return {
        n = 0,
        add = function (self, item)
            self.n = self.n + 1
            self[self.n] = item
        end,
    }
end

local function split(text, delimiter)
    -- Return a numbered table with fields from splitting text.
    -- The delimiter is used in a regex without escaping (for example, '.' would fail).
    -- Each field has any leading/trailing whitespace removed.
    local t = {}
    text = text .. delimiter  -- to get last item
    for item in text:gmatch('%s*(.-)%s*' .. delimiter) do
        table.insert(t, item)
    end
    return t
end

local function strip(text)
    -- If text is a string, return its content with no leading/trailing
    -- whitespace. Otherwise return nil (a nil argument gives a nil result).
    if type(text) == 'string' then
        return text:match("^%s*(.-)%s*$")
    end
end

local function message(mcode)
    -- Return wikitext for an error message, including category if specified
    -- for the message type.
    -- mcode = numbered table specifying the message:
    --    mcode[1] = 'cvt_xxx' (string used as a key to get message info)
    --    mcode[2] = 'parm1' (string to replace first %s if any in message)
    --    mcode[3] = 'parm2' (string to replace second %s if any in message)
    --    mcode[4] = 'parm3' (string to replace third %s if any in message)
    local msg = all_messages[mcode[1]]
    if msg then
        local text = format(msg[1] or 'Missing message',
            mcode[2] or '?',
            mcode[3] or '?',
            mcode[4] or '?')
        local cat = all_categories[msg[2]] or ''
        local prefix = all_messages[msg.warning and 'cvt_prefix_warning' or 'cvt_prefix_error'] or ''
        local suffix = (prefix == '') and '' or '</span>'
        local regex, replace = msg.regex, msg.replace
        if regex and replace then
            text = text:gsub(regex, replace)
        end
        return prefix .. ' ' .. text .. cat .. suffix
    end
    return 'Convert internal error: unknown message'
end

local function add_warning(parms, mcode, text)
    -- If enabled, add a warning that will be displayed after the convert result.
    -- To reduce output noise, only the first warning is displayed.
    if warnings then
        if parms.warnings == nil then
            parms.warnings = message({ mcode, text })
        end
    end
end

local function spell_number(parms, number, numerator, denominator)
    -- Return result of spelling (number, numerator, denominator), or
    -- return nil if spelling is not available or not supported for given text.
    -- Input should use one of these forms:
    --   number  numerator  denominator  example output
    --   ------  ---------  -----------  --------------
    --   string    nil        nil        one point two three
    --   string  string     string       one and two thirds
    --    nil    string     string       two thirds
    if not speller then
        local function get_speller(module)
            return require(module).spell_number
        end
        local success
        success, speller = pcall(get_speller, spell_module)
        if not success or type(speller) ~= 'function' then
            add_warning(parms, 'cvt_spell_unavailable')
            return nil
        end
    end
    local case = parms.opt_spell_upper
    parms.opt_spell_upper = nil  -- only uppercase first number in a multiple unit
    local sp = not parms.opt_sp_us
    local adj = parms.opt_adjectival
    return speller(number, numerator, denominator, case, sp, adj)
end

------------------------------------------------------------------------
-- BEGIN: Code required only for built-in units.
-- LATER: If need much more code, move to another module to simplify this module.
local function speed_of_sound(altitude)
    -- This is for the Mach built-in unit of speed.
    -- Return speed of sound in metres per second at given altitude in feet.
    -- If no altitude given, use default (zero altitude = sea level).
    -- Table gives speed of sound in miles per hour at various altitudes:
    --   altitude = -17,499 to 302,499 feet
    -- mach_table[a + 4] = s where
    --   a = (altitude / 5000) rounded to nearest integer (-3 to 60)
    --   s = speed of sound (mph) at that altitude
    -- LATER: Should calculate result from an interpolation between the next
    -- lower and higher altitudes in table, rather than rounding to nearest.
    -- From: http://www.aerospaceweb.org/question/atmosphere/q0112.shtml
    local mach_table = {                                                       -- a =
        799.5, 787.0, 774.2, 761.207051,                                       -- -3 to  0
        748.0, 734.6, 721.0, 707.0, 692.8, 678.3, 663.5, 660.1, 660.1, 660.1,  --  1 to 10
        660.1, 660.1, 660.1, 662.0, 664.3, 666.5, 668.9, 671.1, 673.4, 675.6,  -- 11 to 20
        677.9, 683.7, 689.9, 696.0, 702.1, 708.1, 714.0, 719.9, 725.8, 731.6,  -- 21 to 30
        737.3, 737.7, 737.7, 736.2, 730.5, 724.6, 718.8, 712.9, 707.0, 701.1,  -- 31 to 40
        695.0, 688.9, 682.8, 676.6, 670.4, 664.1, 657.8, 652.9, 648.3, 643.7,  -- 41 to 50
        639.1, 634.4, 629.6, 624.8, 620.0, 615.2, 613.2, 613.2, 613.2, 613.5,  -- 51 to 60
    }
    altitude = altitude or 0
    local a = (altitude < 0) and -altitude or altitude
    a = floor(a / 5000 + 0.5)
    if altitude < 0 then
        a = -a
    end
    if a < -3 then
        a = -3
    elseif a > 60 then
        a = 60
    end
    return mach_table[a + 4] * 0.44704  -- mph converted to m/s
end
-- END: Code required only for built-in units.
------------------------------------------------------------------------

local function override_from(out_table, in_table, fields)
    -- Copy the specified fields from in_table to out_table, but do not
    -- copy nil fields (keep any corresponding field in out_table).
    for _, field in ipairs(fields) do
        if in_table[field] then
            out_table[field] = in_table[field]
        end
    end
end

local function shallow_copy(t)
    -- Return a shallow copy of table t.
    -- Do not need the features and overhead of the Scribunto mw.clone().
    local result = {}
    for k, v in pairs(t) do
        result[k] = v
    end
    return result
end

local unit_mt = {
    -- Metatable to get missing values for a unit that does not accept SI prefixes,
    -- or for a unit that accepts prefixes but where no prefix was used.
    -- In the latter case, and before use, fields symbol, name1, name1_us
    -- must be set from _symbol, _name1, _name1_us respectively.
    __index = function (self, key)
        local value
        if key == 'name1' or key == 'sym_us' then
            value = self.symbol
        elseif key == 'name2' then
            value = self.name1 .. plural_suffix
        elseif key == 'name1_us' then
            value = self.name1
            if not rawget(self, 'name2_us') then
                -- If name1_us is 'foot', do not make name2_us by appending plural_suffix.
                self.name2_us = self.name2
            end
        elseif key == 'name2_us' then
            local raw1_us = rawget(self, 'name1_us')
            if raw1_us then
                value = raw1_us .. plural_suffix
            else
                value = self.name2
            end
        elseif key == 'link' then
            value = self.name1
        elseif key == 'builtin' then
            value = false
        else
            return nil
        end
        rawset(self, key, value)
        return value
    end
}

local unit_prefixed_mt = {
    -- Metatable to get missing values for a unit that accepts SI prefixes,
    -- and where a prefix has been used.
    -- Before use, fields si_name, si_prefix must be defined.
    __index = function (self, key)
        local value
        if key == 'symbol' then
            value = self.si_prefix .. self._symbol
        elseif key == 'sym_us' then
            value = self.symbol  -- always the same as sym_us for prefixed units
        elseif key == 'name1' then
            -- prefix_position is a byte (not character) position, so use Lua's sub().
            local pos = rawget(self, 'prefix_position') or 1
            value = self._name1
            value = value:sub(1, pos - 1) .. self.si_name .. value:sub(pos)
        elseif key == 'name2' then
            value = self.name1 .. plural_suffix
        elseif key == 'name1_us' then
            value = rawget(self, '_name1_us')
            if value then
                local pos = rawget(self, 'prefix_position') or 1
                value = value:sub(1, pos - 1) .. self.si_name .. value:sub(pos)
            else
                value = self.name1
            end
        elseif key == 'name2_us' then
            if rawget(self, '_name1_us') then
                value = self.name1_us .. plural_suffix
            else
                value = self.name2
            end
        elseif key == 'link' then
            value = self.name1
        elseif key == 'builtin' then
            value = false
        else
            return nil
        end
        rawset(self, key, value)
        return value
    end
}

local unit_per_mt = {
    -- Metatable to get values for a "per" unit of form "x/y".
    -- This is never called to determine a unit name or link because "per" units
    -- are handled as a special case.
    __index = function (self, key)
        local value
        if key == 'symbol' then
            local per = self.per
            local unit1, unit2 = per[1], per[2]
            if unit1 then
                value = unit1[key] .. '/' .. unit2[key]
            else
                value = '/' .. unit2[key]
            end
        elseif key == 'sym_us' then
            value = self.symbol
        elseif key == 'scale' then
            local per = self.per
            local unit1, unit2 = per[1], per[2]
            value = (unit1 and unit1.scale or 1) / unit2.scale
        elseif key == 'builtin' then
            value = false
        else
            return nil
        end
        rawset(self, key, value)
        return value
    end
}

local function lookup(unitcode, opt_sp_us, what, utable, fails, depth)
    -- Return true, t where t is a copy of the unit's converter table,
    -- or return false, t where t is an error message table.
    -- Parameter opt_sp_us is true for US spelling of SI prefixes and
    -- the symbol and name of the unit. If true, the result includes field
    -- sp_us = true (that field may also have been in the unit definition).
    -- Parameter 'what' determines whether combination units are accepted:
    --   'no_combination'  : single unit only
    --   'any_combination' : single unit or combination or output multiple
    --   'only_multiple'   : single unit or output multiple only
    -- Parameter unitcode is a symbol (like 'g'), with an optional SI prefix (like 'kg').
    -- If, for example, 'kg' is in this table, that entry is used;
    -- otherwise the prefix ('k') is applied to the base unit ('g').
    -- If unitcode is a known combination code (and if allowed by what),
    -- a table of output multiple unit tables is included in the result.
    -- For compatibility with the old template, underscores in unitcode are replaced
    -- with spaces so {{convert|350|board_feet}} --> 350 board feet (0.83 m³).
    utable = utable or all_units
    fails = fails or {}
    depth = depth and depth + 1 or 1
    if depth > 9 then
        -- There are ways to mistakenly define units which result in infinite
        -- recursion when lookup() is called. That gives a long delay and very
        -- confusing error messages, so the depth parameter is used as a guard.
        return false, { 'cvt_lookup', unitcode }
    end
    if unitcode == nil or unitcode == '' then
        return false, { 'cvt_no_unit' }
    end
    unitcode = unitcode:gsub('_', ' ')
    local t = utable[unitcode]
    if t then
        if t.shouldbe then
            return false, { 'cvt_should_be', t.shouldbe }
        end
        local force_sp_us = opt_sp_us
        if t.sp_us then
            force_sp_us = true
            opt_sp_us = true
        end
        local target = t.target  -- nil, or unitcode is an alias for this target
        if target then
            local success, result = lookup(target, opt_sp_us, what, utable, fails, depth)
            if not success then return false, result end
            override_from(result, t, { 'customary', 'default', 'link', 'symbol', 'symlink' })
            local multiplier = t.multiplier
            if multiplier then
                result.multiplier = tostring(multiplier)
                result.scale = result.scale * multiplier
            end
            return true, result
        end
        local per = t.per  -- nil/false, or a numbered table for "x/y" units
        if per then
            local result = { utype = t.utype, per = {} }
            override_from(result, t, { 'default', 'invert', 'iscomplex', 'symbol', 'symlink' })
            result.symbol_raw = (result.symbol or false)  -- to distinguish between a defined exception and a metatable calculation
            local cvt = result.per
            local prefix
            for i, v in ipairs(per) do
                if i == 1 and (v == '$' or v == '£') then
                    prefix = v
                else
                    local success, t = lookup(v, opt_sp_us, 'no_combination', utable, fails, depth)
                    if not success then return false, t end
                    cvt[i] = t
                    if t.sp_us then  -- if the top or bottom unit forces sp=us, set the per unit to use the correct name/symbol
                        force_sp_us = true
                    end
                end
            end
            if prefix then
                result.vprefix = prefix
            else
                result.vprefix = false  -- to avoid calling __index
            end
            result.sp_us = force_sp_us
            return true, setmetatable(result, unit_per_mt)
        end
        local combo = t.combination  -- nil or a table of unitcodes
        if combo then
            local multiple = t.multiple
            if what == 'no_combination' or (what == 'only_multiple' and multiple == nil) then
                return false, { 'cvt_bad_unit', unitcode }
            end
            -- Recursively create a combination table containing the
            -- converter table of each unitcode.
            local result = { utype = t.utype, multiple = multiple, combination = {} }
            local cvt = result.combination
            for i, v in ipairs(combo) do
                local success, t = lookup(v, opt_sp_us, multiple and 'no_combination' or 'only_multiple', utable, fails, depth)
                if not success then return false, t end
                cvt[i] = t
            end
            return true, result
        end
        local result = shallow_copy(t)
        result.sp_us = force_sp_us
        if result.prefixes then
            result.symbol = result._symbol
            result.name1 = result._name1
            result.name1_us = result._name1_us
        end
        return true, setmetatable(result, unit_mt)
    end
    for plen = SIprefixes[1] or 2, 1, -1 do
        -- Look for an SI prefix; should never occur with an alias.
        -- Check for longer prefix first ('dam' is decametre).
        -- SIprefixes[1] = prefix maximum #characters (as seen by mw.ustring.sub).
        local prefix = usub(unitcode, 1, plen)
        local si = SIprefixes[prefix]
        if si then
            local t = utable[usub(unitcode, plen+1)]
            if t and t.prefixes then
                local result = shallow_copy(t)
                if opt_sp_us then
                    result.sp_us = true
                end
                if result.sp_us and si.name_us then
                    result.si_name = si.name_us
                else
                    result.si_name = si.name
                end
                result.si_prefix = si.prefix or prefix
                result.scale = t.scale * 10 ^ (si.exponent * t.prefixes)
                return true, setmetatable(result, unit_prefixed_mt)
            end
        end
    end
    -- Accept any unit with an engineering notation prefix like "e6cuft"
    -- (million cubic feet), but not chained prefixes like "e3e6cuft",
    -- and not if the unit is a combination or multiple,
    -- and not if the unit has an offset or is a built-in.
    -- Only en digits are accepted.
    local exponent, baseunit = unitcode:match('^e(%d+)(.*)')
    if exponent then
        local engscale = eng_scales[exponent]
        if engscale then
            local success, result = lookup(baseunit, opt_sp_us, 'no_combination', utable, fails, depth)
            if not success then return false, result end
            if not (result.offset or result.builtin or result.engscale) then
                result.defkey = unitcode  -- key to lookup default exception
                result.engscale = engscale
                result.scale = result.scale * 10 ^ tonumber(exponent)
                return true, result
            end
        end
    end
    if not extra_units then
        local success, extra = pcall(function () return require(extra_module).extra_units end)
        if success and type(extra) == 'table' then
            extra_units = extra
        end
    end
    if extra_units then
        -- A unit in one data table might refer to a unit in the other table, so
        -- switch between them, relying on fails or depth to terminate loops.
        local failed = fails[unitcode]
        if not failed then
            fails[unitcode] = true
            local other = (utable == all_units) and extra_units or all_units
            local success, result = lookup(unitcode, opt_sp_us, what, other, fails, depth)
            if success then
                return true, result
            end
        end
    end
    return false, { 'cvt_unknown', unitcode }
end

local function valid_number(num)
    -- Return true if num is a valid number.
    -- Expressed as a string, overflow or other problems are indicated with
    -- text like "1.#INF" or ".#IND" which are regarded as invalid here.
    if type(num) == 'number' and tostring(num):find('#', 1, true) == nil then
        return true
    end
end

local function ntsh(num, debug)
    -- Return html text to be used for a hidden sort key so that
    -- the given number will be sorted in numeric order.
    -- If debug == true, output is in a box (not hidden).
    -- This implements Template:Ntsh (number table sorting, hidden).
    local result, style
    if not valid_number(num) then
        if num < 0 then
            result = '1000000000000000000'
        else
            result = '9000000000000000000'
        end
    elseif num == 0 then
        result = '5000000000000000000'
    else
        local mag = floor(log10(abs(num)) + 1e-14)
        local prefix
        if num > 0 then
            prefix = 7000 + mag
        else
            prefix = 2999 - mag
            num = num + 10^(mag+1)
        end
        result = format('%d', prefix) .. format('%015.0f', floor(num * 10^(14-mag)))
    end
    if debug then
        style = 'border:1px solid'
    else
        style = 'display:none'
    end
    return '<span style="' .. style .. '">' .. result .. '</span>'
end

local function hyphenated(name)
    -- Return a hyphenated form of given name (for adjectival usage).
    -- This uses a simple and efficient procedure that works for most cases.
    -- Some units (if used) would require more, and can later think about
    -- adding a method to handle exceptions.
    -- The procedure is to replace each space with a hyphen, but
    -- not a space after ')' [for "(pre-1954&nbsp;US) nautical mile"], and
    -- not spaces immediately before '(' or in '(...)' [for cases like
    -- "British thermal unit (ISO)" and "Calorie (International Steam Table)"].
    local pos
    if name:sub(1, 1) == '(' then
        pos = name:find(')', 1, true)
        if pos then
            return name:sub(1, pos+1) .. name:sub(pos+2):gsub(' ', '-')
        end
    elseif name:sub(-1, -1) == ')' then
        pos = name:find('(', 1, true)
        if pos then
            return name:sub(1, pos-2):gsub(' ', '-') .. name:sub(pos-1)
        end
    end
    return name:gsub(' ', '-')
end

local function hyphenated_maybe(parms, want_name, sep, id, inout)
    -- Return s, f where
    --   s = id, possibly modified
    --   f = true if hyphenated
    -- Possible modifications: hyphenate; prepend '-'; append mid text.
    if id == nil or id == '' then
        return ''
    end
    local mid
    if parms.opt_adjectival then
        if inout == (parms.opt_flip and 'out' or 'in') then
            mid = parms.mid
        end
        if want_name then
            return '-' .. hyphenated(id) .. (mid or ''), true
        end
    end
    return sep .. id .. (mid or '')
end

local function change_sign(text)
    -- Change sign of text for correct appearance because it is negated.
    if text:sub(1, 1) == '-' then
        return text:sub(2)
    end
    return '-' .. text
end

local function use_minus(text)
    -- Return text with Unicode minus instead of '-', if present.
    if text:sub(1, 1) == '-' then
        return MINUS .. text:sub(2)
    end
    return text
end

local function digit_grouper(method, gaps)
    -- Return a table to hold groups of digits which can be joined with
    -- suitable separators (such as commas).
    -- Each group is separately translated to the local language because the
    -- separators may include '.' characters which should not be translated.
    -- Parameter method is a number or nil:
    --   3 for 3-digit grouping, or
    --   2 for 3-then-2 grouping.
    -- Parameter gaps is true to use <span> gaps (numsep ignored).
    return {
        n = 0,
        add = function (self, digits)
            self.n = self.n + 1
            self[self.n] = from_en(digits)
        end,
        join = function (self, rhs)
            -- Concatenate in reverse order.
            if gaps then
                local result = ''
                for i = 1, self.n - 1 do
                    result = '<span style="margin-left: 0.25em">' .. self[i] .. '</span>' .. result
                end
                return '<span style="white-space: nowrap">' .. self[self.n] .. result .. from_en(rhs) .. '</span>'
            else
                local result = self[1]
                for i = 2, self.n do
                    result = self[i] .. numsep .. result
                end
                return result .. from_en(rhs)
            end
        end,
        step = 3,
        next_position = function (self, previous)
            -- Return position of digit just before next group.
            -- Digits are grouped from right-to-left (least significant first).
            local result = previous - self.step
            if method == 2 then
                self.step = 2  -- may need more (3, 2, 2, 3, 2, 2, ...) in some languages
            end
            return (result < 0) and 0 or result
        end,
    }
end

local function with_separator(parms, text)
    -- Input text is a number in en digits and with '.' decimal mark.
    -- Return an equivalent of text, formatted for display:
    --   with a custom decimal mark instead of '.', if wanted
    --   with thousand separators inserted, if wanted
    --   digits in local language
    -- The given text is like '123' or '12345.6789' or '1.23e45'
    -- (e notation can only occur when processing an input value).
    -- The text has no sign (caller inserts that later, if necessary).
    -- Separator is inserted only in the integer part of the significand
    -- (not after the decimal mark, and not after 'e' or 'E').
    if parms.opt_nocomma or numsep == '' then
        return from_en(text)
    end
    local last = text:match('()[.eE]')  -- () returns position
    if last == nil then
        last = #text
    else
        last = last - 1  -- index of last character before dot/e/E
    end
    if last < 4 or (last == 4 and parms.opt_comma5) then
        return from_en(text)
    end
    local groups = digit_grouper(group_method, parms.opt_gaps)
    local i = last
    while i > 0 do
        local position = groups:next_position(i)
        groups:add(text:sub(position+1, i))
        i = position
    end
    return groups:join(text:sub(last+1))
end

-- Input values can use values like 1.23e12, but are never displayed
-- using scientific notation like 1.23×10¹².
-- Very small or very large output values use scientific notation.
-- Use format(fmtpower, significand, '10', exponent) where each arg is a string.
local fmtpower = '%s<span style="margin:0 .15em 0 .25em">×</span>%s<sup>%s</sup>'

local function with_exponent(show, exponent)
    -- Return wikitext to display the implied value in scientific notation.
    -- Input uses en digits; output uses digits in local language.
    if #show > 1 then
        show = show:sub(1, 1) .. '.' .. show:sub(2)
    end
    return format(fmtpower, from_en(show), from_en('10'), use_minus(from_en(tostring(exponent))))
end

local function make_sigfig(value, sigfig)
    -- Return show, exponent that are equivalent to the result of
    -- converting the number 'value' (where value >= 0) to a string,
    -- rounded to 'sigfig' significant figures.
    -- The returned items are:
    --   show: a string of digits; no sign and no dot;
    --         there is an implied dot before show.
    --   exponent: a number (an integer) to shift the implied dot.
    -- Resulting value = tonumber('.' .. show) * 10^exponent.
    -- Examples:
    --   make_sigfig(23.456, 3) returns '235', 2 (.235 * 10^2).
    --   make_sigfig(0.0023456, 3) returns '235', -2 (.235 * 10^-2).
    --   make_sigfig(0, 3) returns '000', 1 (.000 * 10^1).
    if sigfig <= 0 then
        sigfig = 1
    elseif sigfig > maxsigfig then
        sigfig = maxsigfig
    end
    if value == 0 then
        return string.rep('0', sigfig), 1
    end
    local exp, frac = math.modf(log10(value))
    if frac >= 0 then
        frac = frac - 1
        exp = exp + 1
    end
    local digits = format('%.0f', 10^(frac + sigfig))
    if #digits > sigfig then
        -- Overflow (for sigfig=3: like 0.9999 rounding to "1000"; need "100").
        digits = digits:sub(1, sigfig)
        exp = exp + 1
    end
    assert(#digits == sigfig, 'Bug: rounded number has wrong length')
    return digits, exp
end

local function format_number(parms, show, exponent, isnegative)
    -- Parameter show is a number in en digits and with '.' decimal mark.
    -- Return t where t is a table with fields:
    --   show = wikitext formatted to display implied value
    --          (digits in local language)
    --   is_scientific = true if show uses scientific notation
    --   clean = unformatted show (possibly adjusted and with inserted '.')
    --          (en digits)
    --   sign = '' or MINUS
    --   exponent = exponent (possibly adjusted)
    -- The clean and exponent fields can be used to calculate the
    -- rounded absolute value, if needed.
    --
    -- The value implied by the arguments is found from:
    --   exponent is nil; and
    --   show is a string of digits (no sign), with an optional dot;
    --   show = '123.4' is value 123.4, '1234' is value 1234.0;
    -- or:
    --   exponent is an integer indicating where dot should be;
    --   show is a string of digits (no sign and no dot);
    --   there is an implied dot before show;
    --   show does not start with '0';
    --   show = '1234', exponent = 3 is value 0.1234*10^3 = 123.4.
    --
    -- The formatted result:
    -- * Is for an output value and is spelled if wanted and possible.
    -- * Includes a Unicode minus if isnegative.
    -- * Uses a custom decimal mark, if wanted.
    -- * Has digits grouped where necessary, if wanted.
    -- * Uses scientific notation for very small or large values
    --   (which forces output to not be spelled).
    -- * Has no more than maxsigfig significant digits
    --   (same as old template and {{#expr}}).
    local sign = isnegative and MINUS or ''
    local maxlen = maxsigfig
    if exponent == nil then
        local integer, dot, fraction = show:match('^(%d*)(%.?)(.*)')
        if #integer >= 10 then
            show = integer .. fraction
            exponent = #integer
        elseif integer == '0' or integer == '' then
            local zeros, figs = fraction:match('^(0*)([^0]?.*)')
            if #figs == 0 then
                if #zeros > maxlen then
                    show = '0.' .. zeros:sub(1, maxlen)
                end
            elseif #zeros >= 4 then
                show = figs
                exponent = -#zeros
            elseif #figs > maxlen then
                show = '0.' .. zeros .. figs:sub(1, maxlen)
            end
        else
            maxlen = maxlen + #dot
            if #show > maxlen then
                show = show:sub(1, maxlen)
            end
        end
    end
    if exponent then
        if #show > maxlen then
            show = show:sub(1, maxlen)
        end
        if exponent > 10 or exponent <= -4 or (exponent == 10 and show ~= '1000000000') then
            -- Rounded value satisfies: value >= 1e9 or value < 1e-4 (1e9 = 0.1e10).
            return {
                clean = '.' .. show,
                exponent = exponent,
                sign = sign,
                show = sign .. with_exponent(show, exponent-1),
                is_scientific = true,
            }
        end
        if exponent >= #show then
            show = show .. string.rep('0', exponent - #show)  -- result has no dot
        elseif exponent <= 0 then
            show = '0.' .. string.rep('0', -exponent) .. show
        else
            show = show:sub(1, exponent) .. '.' .. show:sub(exponent+1)
        end
    end
    if isnegative and show:match('^0.?0*$') then
        sign = ''  -- don't show minus if result is negative but rounds to zero
    end
    local formatted_show = sign .. with_separator(parms, show)
    if parms.opt_spell_out then
        formatted_show = spell_number(parms, sign .. show) or formatted_show
    end
    return {
        clean = show,
        sign = sign,
        show = formatted_show,
    }
end

-- Fraction output format.
-- 2013-07-20 Trying new styles proposed at [[Template talk:Convert]].
local fracfmt = {
 { -- Like {{frac}} (fraction slash).
   -- 1/2    : sign, numerator, denominator
   -- 1+2/3  : signed_wholenumber, numerator, denominator
   '<span class="frac nowrap">%s<sup>%s</sup>&frasl;<sub>%s</sub></span>',
   '<span class="frac nowrap">%s<sup> %s</sup>&frasl;<sub>%s</sub></span>',
 },
 { -- Like {{sfrac}} (fraction horizontal bar).
   -- 1//2   : sign, numerator, denominator (sign should probably be before the fraction, but then it can wrap, and html is already too long)
   -- 1+2//3 : signed_wholenumber, numerator, denominator
   '<span class="sfrac nowrap" style="display:inline-block; vertical-align:-0.5em; font-size:85%%; text-align:center;"><span style="display:block; line-height:1em; padding:0 0.1em;">%s%s</span><span style="display:none;">/</span><span style="display:block; line-height:1em; padding:0 0.1em; border-top:1px solid;">%s</span></span>',
   '<span class="sfrac nowrap">%s<span style="display:none;">&nbsp;</span><span style="display:inline-block; vertical-align:-0.5em; font-size:85%%; text-align:center;"><span style="display:block; line-height:1em; padding:0 0.1em;">%s</span><span style="display:none;">/</span><span style="display:block; line-height:1em; padding:0 0.1em; border-top:1px solid;">%s</span></span></span>',
 },
 { -- Like old {{convert}} template.
   -- 1///2  : sign, numerator, denominator
   -- 1+2///3: signed_wholenumber, sign, numerator, denominator
   '<span style="white-space:nowrap">%s<sup>%s</sup>&frasl;<sub>%s</sub></span>',
   '<span class="frac nowrap">%s<s style="display:none">%s</s><sup>%s</sup>&frasl;<sub>%s</sub></span>',
 },
}

local function extract_fraction(parms, text, negative)
    -- If text represents a fraction, return value, show, spelled where
    --   value is a number (value of the fraction in argument text)
    --   show is a string (formatted text for display of an input value,
    --        and is spelled if wanted and possible)
    --   spelled is true if show was spelled
    -- Otherwise, return nil.
    -- Input uses en digits and '.' decimal mark (input has been translated).
    -- Output uses digits in local language and custom decimal mark, if any.
    --
    -- In the following, '(3/8)' represents the wikitext required to
    -- display a fraction with numerator 3 and denominator 8.
    -- In the wikitext, Unicode minus is used for a negative value.
    --   text          value, show            value, show
    --                 if not negative       if negative
    --   3 / 8         0.375, '(3/8)'        -0.375, '−(3/8)'
    --   2 + 3 / 8     2.375, '2(3/8)'       -1.625, '−2(−3/8)'
    --   2 - 3 / 8     1.625, '2(−3/8)'      -2.375, '−2(3/8)'
    --   1 + 20/8      3.5  , '1/(20/8)'     1.5   , '−1/(−20/8)'
    --   1 - 20/8      -1.5., '1(−20/8)'     -3.5  , '−1(20/8)'
    -- Wherever an integer appears above, numbers like 1.25 or 12.5e-3
    -- (which may be negative) are also accepted (like old template).
    -- Template interprets '1.23e+2+12/24' as '123(12/24)' = 123.5!
    local numstr, whole, value
    local lhs, slash, denstr = text:match('^%s*([^/]-)%s*(/+)%s*(.-)%s*$')
    local denominator = tonumber(denstr)
    if denominator == nil then return nil end
    local wholestr, negfrac, rhs = lhs:match('^%s*(.-[^eE])%s*([+-])%s*(.-)%s*$')
    if wholestr == nil or wholestr == '' then
        wholestr = nil
        whole = 0
        numstr = lhs
    else
        whole = tonumber(wholestr)
        if whole == nil then return nil end
        numstr = rhs
    end
    negfrac = (negfrac == '-')
    local numerator = tonumber(numstr)
    if numerator == nil then return nil end
    -- Spelling of silly inputs like "-2+3/8" or "2+3/+8" (mixed or excess signs) is not supported.
    local do_spell
    if negative == negfrac or wholestr == nil then
        value = whole + numerator / denominator
        do_spell = parms.opt_spell_in
        if do_spell then
            if not (numstr:match('^%d') and denstr:match('^%d')) then  -- if either has a sign
                do_spell = false
            end
        end
    else
        value = whole - numerator / denominator
        numstr = change_sign(numstr)
        do_spell = false
    end
    if not valid_number(value) then
        return nil  -- overflow or similar
    end
    numstr = use_minus(numstr)
    denstr = use_minus(denstr)
    local style = #slash  -- kludge: 1, 2, or 3 slashes can be used to select style
    if style > 3 then style = 3 end
    local wikitext
    if wholestr then
        if negative then
            wholestr = change_sign(wholestr)
        end
        local fmt = fracfmt[style][2]
        if style < 3 then
            wikitext = format(fmt, use_minus(from_en(wholestr)), from_en(numstr), from_en(denstr))
        else
            local sign = negative and MINUS or '+'
            wikitext = format(fmt, use_minus(from_en(wholestr)), sign, from_en(numstr), from_en(denstr))
        end
    else
        local sign = negative and MINUS or ''
        wikitext = format(fracfmt[style][1], sign, from_en(numstr), from_en(denstr))
    end
    if do_spell then
        local numsign = (wholestr or not negative) and '' or '-'
        wikitext = spell_number(parms, wholestr, numsign .. numstr, denstr) or wikitext
    end
    return value, wikitext, do_spell
end

local function extract_number(parms, text, another, no_fraction)
    -- Return true, info if can extract a number from text,
    -- where info is a table with the result,
    -- or return false, t where t is an error message table.
    -- Input can use en digits or digits in local language.
    -- Parameter another = true if the expected value is not the first.
    -- Before processing, the input text is cleaned:
    -- * Any thousand separators (valid or not) are removed.
    -- * Any sign (and optional following whitespace) is replaced with
    --   '-' (if negative) or '' (otherwise).
    --   That replaces Unicode minus with '-'.
    -- If successful, the returned info table contains named fields:
    --   value    = a valid number
    --   singular = true if value is 1 (to use singular form of units)
    --            = false if value is -1 (like old template)
    --   clean    = cleaned text with any separators and sign removed
    --              (en digits and '.' decimal mark)
    --   show     = text formatted for output
    --              (digits in local language and custom decimal mark)
    -- The resulting show:
    -- * Is for an input value and is spelled if wanted and possible.
    -- * Has a rounded value, if wanted.
    -- * Has digits grouped where necessary, if wanted.
    -- * If negative, a Unicode minus is used; otherwise the sign is
    --   '+' (if the input text used '+'), or is '' (if no sign in input).
    text = strip(text or '')
    local clean = to_en(text)
    if clean == '' then
        return false, { another and 'cvt_no_num2' or 'cvt_no_num' }
    end
    local isnegative, propersign = false, ''  -- most common case
    local singular, show
    local value = tonumber(clean)
    if value then
        local sign = clean:sub(1, 1)
        if sign == '+' or sign == '-' then
            propersign = (sign == '+') and '+' or MINUS
            clean = clean:sub(2)
        end
        if value < 0 then
            isnegative = true
            value = -value
        end
    else
        local valstr
        for _, prefix in ipairs({ '-', MINUS, '&minus;' }) do
            -- Including '-' means inputs like '- 2' (with space) are accepted as -2.
            -- It also sets isnegative in case input is a fraction like '-2-3/4'.
            local plen = #prefix
            if clean:sub(1, plen) == prefix then
                valstr = clean:sub(plen + 1)
                break
            end
        end
        if valstr then
            isnegative = true
            propersign = MINUS
            clean = valstr
            value = tonumber(clean)
        end
        if value == nil then
            local spelled
            if not no_fraction then
                value, show, spelled = extract_fraction(parms, clean, isnegative)
            end
            if value == nil then
                return false, { 'cvt_bad_num', text }
            end
            if spelled and value <= 1 then
                singular = true  -- for example, "one half mile" (singular unit)
            else
                singular = false -- any numeric fraction (even with value 1) is regarded as plural
            end
        end
    end
    if not valid_number(value) then  -- for example, "1e310" overflows
        return false, { 'cvt_invalid_num' }
    end
    if show == nil then
        singular = (value == 1 and not isnegative)
        local precision = parms.input_precision
        if precision and 0 <= precision and precision <= 8 then
            value = value + 2e-14  -- fudge for some common cases of bad rounding
            local fmt = '%.' .. format('%d', precision) .. 'f'
            show = fmt:format(value)
        else
            show = clean
        end
        show = propersign .. with_separator(parms, show)
        if parms.opt_spell_in then
            show = spell_number(parms, propersign .. clean) or show
        end
    end
    if isnegative and (value ~= 0) then
        value = -value
    end
    return true, {
        value = value,
        singular = singular,
        clean = clean,
        show = show,
    }
end

local function get_number(text)
    -- Return v, f where:
    --   v = nil (text is not a number)
    -- or
    --   v = value of text (text is a number)
    --   f = true if value is an integer
    -- Input can use en digits or digits in local language,
    -- but no separators, no Unicode minus, and no fraction.
    if text then
        local number = tonumber(to_en(text))
        if number then
            local integer, fraction = math.modf(number)
            return number, (fraction == 0)
        end
    end
end

local function preunits(count, preunit1, preunit2)
    -- If count is 1:
    --     ignore preunit2
    --     return p1
    -- else:
    --     preunit1 is used for preunit2 if the latter is empty
    --     return p1, p2
    -- where:
    --     p1 is text to insert before the input unit
    --     p2 is text to insert before the output unit
    --     p1 or p2 may be nil to mean "no preunit"
    -- Using '+ ' gives output like "5+ feet" (no preceding space).
    local function withspace(text, i)
        -- Insert space at beginning if i == 1, or at end if i == -1.
        -- However, no space is inserted if there is a space or '&nbsp;'
        -- or '-' at that position ('-' is for adjectival text).
        local current = text:sub(i, i)
        if current == ' ' or current == '-' then
            return text
        end
        if i == 1 then
            current = text:sub(1, 6)
        else
            current = text:sub(-6, -1)
        end
        if current == '&nbsp;' then
            return text
        end
        if i == 1 then
            return ' ' .. text
        end
        return text .. ' '
    end
    preunit1 = preunit1 or ''
    local trim1 = strip(preunit1)
    if count == 1 then
        if trim1 == '' then
            return nil
        end
        return withspace(withspace(preunit1, 1), -1)
    end
    preunit2 = preunit2 or ''
    local trim2 = strip(preunit2)
    if trim1 == '' and trim2 == '' then
        return nil, nil
    end
    if trim1 ~= '+' then
        preunit1 = withspace(preunit1, 1)
    end
    if trim2 == '&#32;' then  -- trick to make preunit2 empty
        preunit2 = nil
    elseif trim2 == '' then
        preunit2 = preunit1
    elseif trim2 ~= '+' then
        preunit2 = withspace(preunit2, 1)
    end
    return preunit1, preunit2
end

local function range_text(range, want_name, parms, before, after)
    -- Return before .. rtext .. after
    -- where rtext is the text that separates two values in a range.
    local rtext, adj_text, exception
    if type(range) == 'table' then
        -- Table must specify range text for abbr=off and for abbr=on,
        -- and may specify range text for 'adj=on',
        -- and may specify exception = true.
        rtext = range[want_name and 'off' or 'on']
        adj_text = range['adj']
        exception = range['exception']
    else
        rtext = range
    end
    if parms.opt_adjectival then
        if want_name or (exception and parms.abbr_org == 'on') then
            rtext = adj_text or rtext:gsub(' ', '-'):gsub('&nbsp;', '-')
        end
    end
    if rtext == '–' and after:sub(1, #MINUS) == MINUS then
        rtext = '&nbsp;– '
    end
    return before .. rtext .. after
end

local function get_composite(parms, iparm, total, in_unit_table)
    -- Look for a composite input unit. For example, "{{convert|1|yd|2|ft|3|in}}"
    -- would result in a call to this function with
    --   iparm = 3 (parms[iparm] = "2", just after the first unit)
    --   total = 1 (number of yards)
    --   in_unit_table = (unit table for "yd")
    -- Return true, iparm, unit where
    --   iparm = index just after the composite units (7 in above example)
    --   unit = composite unit table holding all input units,
    -- or return true if no composite unit is present in parms,
    -- or return false, t where t is an error message table.
    local default, subinfo
    local composite_units, count = { in_unit_table }, 1
    local fixups = {}
    local subunit = in_unit_table
    while subunit.subdivs do  -- subdivs is nil or a table of allowed subdivisions
        local subcode = strip(parms[iparm+1])
        local subdiv = subunit.subdivs[subcode]
        if not subdiv then
            break
        end
        local success
        success, subunit = lookup(subcode, parms.opt_sp_us, 'no_combination')
        if not success then return false, subunit end  -- should never occur
        success, subinfo = extract_number(parms, parms[iparm])
        if not success then return false, subinfo end
        iparm = iparm + 2
        subunit.inout = 'in'
        subunit.valinfo = { subinfo }
        -- Recalculate total as a number of subdivisions.
        -- subdiv[1] = number of subdivisions per previous unit (integer > 1).
        total = total * subdiv[1] + subinfo.value
        if not default then  -- set by the first subdiv with a default defined
            default = subdiv.default
        end
        count = count + 1
        composite_units[count] = subunit
        if subdiv.unit or subdiv.name then
            fixups[count] = { unit = subdiv.unit, name = subdiv.name, valinfo = subunit.valinfo }
        end
    end
    if count == 1 then
        return true  -- no error and no composite unit
    end
    for i, fixup in pairs(fixups) do
        local unit = fixup.unit
        local name = fixup.name
        if not unit or (count > 2 and name) then
            composite_units[i].fixed_name = name
        else
            local success, alternate = lookup(unit, parms.opt_sp_us, 'no_combination')
            if not success then return false, alternate end  -- should never occur
            alternate.inout = 'in'
            alternate.valinfo = fixup.valinfo
            composite_units[i] = alternate
        end
    end
    return true, iparm, {
        utype = in_unit_table.utype,
        scale = subunit.scale,  -- scale of last (least significant) unit
        valinfo = { { value = total, clean = subinfo.clean } },
        composite = composite_units,
        default = default or in_unit_table.default
    }
end

local function translate_parms(parms, named_keys)
    -- Update fields in parms by translating parameters to those used at enwiki.
    -- Also, checks are performed which may display warnings, if enabled.
    -- Return true if successful or return false, t where t is an error message table.
    for _, loc_name in ipairs(named_keys) do
        local loc_value = parms[loc_name]
        local en_name = en_option_name[loc_name]
        if en_name then
            local en_value
            if en_name == 'sigfig' then
                if loc_value == '' then
                    add_warning(parms, 'cvt_empty_option', loc_name)
                else
                    local number, is_integer = get_number(loc_value)
                    if not number or not is_integer or number <= 0 then
                        return false, { 'cvt_bad_sigfig', loc_value }
                    end
                    en_value = number
                end
            else
                en_value = en_option_value[en_name][loc_value]
            end
            if en_value == nil then
                if loc_value == '' then
                    add_warning(parms, 'cvt_empty_option', loc_name)
                else
                    -- Using, for example, aliases like |sing=off|adj=on can give
                    -- loc_value == nil when adj is processed after sing. In that case,
                    -- the following gives a slightly misleading but reasonable warning.
                    local text = loc_value and (loc_name .. '=' .. loc_value) or loc_name
                    add_warning(parms, 'cvt_unknown_option', text)
                end
            elseif en_value == '' then
                en_value = nil  -- an ignored option like adj=off
            elseif type(en_value) == 'string' and en_value:sub(1, 4) == 'opt_' then
                for _, v in ipairs(split(en_value, ',')) do
                    parms[v] = true
                end
                en_value = nil
            end
            parms[en_name] = en_value
        else
            add_warning(parms, 'cvt_unknown_option', loc_name .. '=' .. loc_value)
        end
    end
    if parms.adj then
        if parms.adj:sub(1, 2) == 'ri' then
            -- It is known that adj is 'ri1' or 'ri2' or 'ri3', so precision is valid.
            -- Only en digits are accepted.
            parms.input_precision = tonumber(parms.adj:sub(-1))
            parms.adj = nil
        end
    end
    if parms.abbr then
        parms.abbr_org = parms.abbr  -- original abbr that was set, before any flip
    else
        parms.abbr = 'out'  -- default is to abbreviate output only (use symbol, not name)
    end
    if parms.opt_flip then
        local function swap_in_out(option)
            local value = parms[option]
            if value == 'in' then
                parms[option] = 'out'
            elseif value == 'out' then
                parms[option] = 'in'
            end
        end
        swap_in_out('abbr')
        swap_in_out('lk')
        if parms.opt_spell_in then
            -- For simplicity, and because it does not appear to be needed,
            -- user cannot set an option to spell the output.
            parms.opt_spell_in = nil
            parms.opt_spell_out = true
        end
    end
    if parms.opt_table or parms.opt_tablecen then
        if parms.abbr_org == nil and parms.lk == nil then
            parms.opt_values = true
        end
        local align = format('align="%s"', parms.opt_table and 'right' or 'center')
        parms.table_joins = { align .. '|', '\n|' .. align .. '|' }
    end
    if parms.opt_lang_en then
        from_en_table = nil
    end
    return true
end

local function get_values(parms)
    -- If successful, update parms and return true, v, i where
    --   v = table of input values
    --   i = index to next entry in parms after those processed here
    -- or return false, t where t is an error message table.
    local valinfo = collection()  -- numbered table of input values
    local range = collection()  -- numbered table of range items (having, for example, 2 range items requires 3 input values)
    local had_nocomma  -- true if removed "nocomma" kludge from second parameter (like "tonocomma")
    local parm2 = strip(parms[2])
    if parm2 and parm2:sub(-7, -1) == 'nocomma' then
        parms[2] = strip(parm2:sub(1, -8))
        parms.opt_nocomma = true
        had_nocomma = true
    end
    local i = 1
    while true do
        local success, info = extract_number(parms, parms[i], i > 1)  -- need to set parms.opt_nocomma before calling this
        if not success then return false, info end
        i = i + 1
        valinfo:add(info)
        local next = strip(parms[i])
        local range_item = range_types[next] or range_types[range_aliases[next]]
        if not range_item then
            break
        end
        i = i + 1
        range:add(range_item)
        parms.is_range_x = (type(range_item) == 'table') and range_item.is_range_x or nil
    end
    if range.n > 0 then
        if range.n > 30 then  -- limit abuse, although 4 is a more likely upper limit
            return false, { 'cvt_invalid_num' }  -- misleading message but it will do
        end
        parms.range = range
    elseif had_nocomma then
        return false, { 'cvt_unknown', parm2 }
    end
    return true, valinfo, i
end

local function get_parms(pframe)
    -- If successful, return true, parms, unit where
    --   parms is a table of all arguments passed to the template
    --        converted to named arguments, and
    --   unit is the input unit table;
    -- or return false, t where t is an error message table.
    -- MediaWiki removes leading and trailing whitespace from the values of
    -- named arguments. However, the values of numbered arguments include any
    -- whitespace entered in the template, and whitespace is used by some
    -- parameters (example: the numbered parameters associated with "disp=x").
    local parms = {}  -- arguments passed to template
    local named_keys = collection()  -- numbered table of named keys in parms: needed because cannot iterate parms and add new fields to it
    for k, v in pairs(pframe.args) do
        parms[k] = v
        if type(k) == 'string' then
            named_keys:add(k)
        end
    end
    local success, msg = translate_parms(parms, named_keys)
    if not success then return false, msg end
    local success, valinfo, i = get_values(parms)
    if not success then return false, valinfo end
    local in_unit = strip(parms[i])
    i = i + 1
    local success, in_unit_table = lookup(in_unit, parms.opt_sp_us, 'no_combination')
    if not success then return false, in_unit_table end
    if parms.test == 'msg' then
        -- Am testing the messages produced when no output unit is specified, and
        -- the input unit has a missing or invalid default.
        -- Set two units for testing that.
        -- LATER: Remove this code.
        if in_unit == 'chain' then
            in_unit_table.default = nil  -- no default
        elseif in_unit == 'rd' then
            in_unit_table.default  = "ft!X!m"  -- an invalid expression
        end
    end
    in_unit_table.valinfo = valinfo
    in_unit_table.inout = 'in'  -- this is an input unit
    if not parms.range then
        local success, inext, composite_unit = get_composite(parms, i, valinfo[1].value, in_unit_table)
        if not success then return false, inext end
        if composite_unit then
            in_unit_table = composite_unit
            i = inext
        end
    end
    if in_unit_table.builtin == 'mach' then
        -- As with old template, a number following Mach as the input unit is the altitude,
        -- and there is no way to specify an altitude for the output unit.
        -- Could put more code in this function to get any output unit and check for
        -- an altitude following that unit.
        local success, info = extract_number(parms, parms[i], false, true)
        if success then
            i = i + 1
            in_unit_table.altitude = info.value
        end
    end
    local next = strip(parms[i])
    i = i + 1
    local precision, is_bad_precision
    local function set_precision(text)
        local number, is_integer = get_number(text)
        if number then
            if is_integer then
                precision = number
            else
                precision = text
                is_bad_precision = true
            end
            return true  -- text was used for precision, good or bad
        end
    end
    if not set_precision(next) then
        parms.out_unit = next
        if set_precision(strip(parms[i])) then
            i = i + 1
        end
    end
    if parms.opt_adj_mid then
        parms.opt_adjectival = true
        next = parms[i]
        i = i + 1
        if next then  -- mid-text words
            if next:sub(1, 1) == '-' then
                parms.mid = next
            else
                parms.mid = ' ' .. next
            end
        end
    end
    if parms.opt_one_preunit then
        parms[parms.opt_flip and 'preunit2' or 'preunit1'] = preunits(1, parms[i])
        i = i + 1
    end
    if parms.disp == 'x' then
        -- Following is reasonably compatible with the old template.
        local first = parms[i] or ''
        local second = parms[i+1] or ''
        i = i + 2
        if strip(first) == '' then  -- user can enter '&#32;' rather than ' ' to avoid the default
            first = ' [&nbsp;' .. first
            second = '&nbsp;]' .. second
        end
        parms.joins = { first, second }
    elseif parms.opt_two_preunits then
        local p1, p2 = preunits(2, parms[i], parms[i+1])
        i = i + 2
        if parms.preunit1 then
            -- To simplify documentation, allow unlikely use of adj=pre with disp=preunit
            -- (however, an output unit must be specified with adj=pre and with disp=preunit).
            parms.preunit1 = parms.preunit1 .. p1
            parms.preunit2 = p2
        else
            parms.preunit1, parms.preunit2 = p1, p2
        end
    end
    if precision == nil then
        if set_precision(strip(parms[i])) then
            i = i + 1
        end
    end
    if is_bad_precision then
        return false, { 'cvt_bad_prec', precision }
    end
    parms.precision = precision
    return true, parms, in_unit_table
end

local function default_precision(invalue, inclean, outvalue, in_current, out_current, extra)
    -- Return a default value for precision (an integer like 2, 0, -2).
    -- Code follows procedures used in old template.
    local fudge = 1e-14  -- {{Order of magnitude}} adds this, so we do too
    local prec, minprec, adjust
    local utype = out_current.utype
    local subunit_ignore_trailing_zero
    local subunit_more_precision  -- kludge for "in" used in input like "|2|ft|6|in"
    local composite = in_current.composite
    if composite then
        subunit_ignore_trailing_zero = true  -- input "|2|st|10|lb" has precision 0, not -1
        if composite[#composite].exception == 'subunit_more_precision' then
            subunit_more_precision = true  -- do not use standard precision with input like "|2|ft|6|in"
        end
    end
    -- Count digits after decimal mark, handling cases like '12.345e6'.
    local exponent
    local integer, dot, fraction, expstr = inclean:match('^(%d*)(%.?)(%d*)(.*)')
    local e = expstr:sub(1, 1)
    local boost = 0  -- can increase default precision
    if e == 'e' or e == 'E' then
        exponent = tonumber(expstr:sub(2))
    elseif expstr:find('/', 1, true) then
        boost = 1  -- any input fraction is regarded as one extra digit of precision
    end
    if dot == '' then
        prec = subunit_ignore_trailing_zero and 0 or -integer:match('0*$'):len()
    else
        prec = #fraction
    end
    if exponent then
        -- So '1230' and '1.23e3' both give prec = -1, and '0.00123' and '1.23e-3' give 5.
        prec = prec - exponent
    end
    local exception = (utype == 'temperature' and not
            (in_current.exception == 'temperature' or out_current.exception == 'temperature'))
    if exception then
        -- Kelvin value can be almost zero, or small but negative due to precision problems.
        -- Also, an input value like -300 C (below absolute zero) gives negative kelvins.
        -- Calculate minimum precision from absolute value.
        adjust = 0
        local kelvin = abs((invalue - in_current.offset) * in_current.scale)
        if kelvin < 1e-8 then  -- assume nonzero due to input or calculation precision problem
            minprec = 2
        else
            minprec = 2 - floor(log10(kelvin) + fudge)  -- 3 sigfigs in kelvin
        end
    else
        if invalue == 0 or outvalue <= 0 then
            -- We are never called with a negative outvalue, but it might be zero.
            -- This is special-cased to avoid calculation exceptions.
            return 0
        end
        if out_current.exception == 'integer_more_precision' and floor(invalue) == invalue then
            -- With certain output units that sometimes give poor results
            -- with default rounding, use more precision when the input
            -- value is equal to an integer. An example of a poor result
            -- is when input 50 gives a smaller output than input 49.5.
            -- Experiment shows this helps, but it does not eliminate all
            -- surprises because it is not clear whether "50" should be
            -- interpreted as "from 45 to 55" or "from 49.5 to 50.5".
            adjust = -log10(in_current.scale)
        elseif subunit_more_precision then
            -- Conversion like "{{convert|6|ft|1|in|cm}}" (where subunit is "in")
            -- has a non-standard adjust value, to give more output precision.
            adjust = log10(out_current.scale) + 2
        else
            adjust = log10(abs(invalue / outvalue))
        end
        adjust = adjust + log10(2)
        -- Ensure that the output has at least two significant figures.
        minprec = 1 - floor(log10(outvalue) + fudge)
    end
    if extra then
        adjust = extra.adjust or adjust
        minprec = extra.minprec or minprec
    end
    return math.max(floor(prec + adjust + boost), minprec)
end

local function convert(invalue, inclean, in_current, out_current)
    -- Convert given input value from one unit to another.
    -- Return output_value (a number) if a simple convert, or
    -- return f, t where
    --   f = true, t = table of information with results, or
    --   f = false, t = error message table.
    local inscale = in_current.scale
    local outscale = out_current.scale
    if not in_current.iscomplex and not out_current.iscomplex then
        return invalue * (inscale / outscale)  -- minimize overhead for most common case
    end
    if in_current.invert then
        -- Fuel efficiency (there are no built-ins for this type of unit).
        if in_current.invert * out_current.invert < 0 then
            return 1 / (invalue * inscale * outscale)
        end
        return invalue * (inscale / outscale)
    elseif in_current.offset then
        -- Temperature (there are no built-ins for this type of unit).
        return (invalue - in_current.offset) * (inscale / outscale) + out_current.offset
    else
        -- Built-in unit.
        local in_builtin = in_current.builtin
        local out_builtin = out_current.builtin
        if in_builtin and out_builtin then
            if in_builtin == out_builtin then
                return invalue
            end
            -- There are no cases (yet) where need to convert from one
            -- built-in unit to another, so this should never occur.
            return false, { 'cvt_bug_convert' }
        end
        if in_builtin == 'mach' or out_builtin == 'mach' then
            local adjust
            if in_builtin == 'mach' then
                inscale = speed_of_sound(in_current.altitude)
                adjust = outscale / 0.1
            else
                outscale = speed_of_sound(out_current.altitude)
                adjust = 0.1 / inscale
            end
            return true, {
                outvalue = invalue * (inscale / outscale),
                adjust = log10(adjust) + log10(2),
            }
        elseif in_builtin == 'hand' then
            -- 1 hand = 4 inches; 1.2 hands = 6 inches.
            -- Fractions of a hand are only defined for the first digit, and
            -- the first fractional digit should be a number of inches (1, 2 or 3).
            -- However, this code interprets the entire fraction as the number
            -- of inches / 10 (so 1.75 inches would be 0.175 hands).
            -- A value like 12.3 hands is exactly 12*4 + 3 inches; base default precision on that.
            local integer, fraction = math.modf(invalue)
            local outvalue = (integer + 2.5 * fraction) * (inscale / outscale)
            local inch_value = 4 * integer + 10 * fraction  -- equivalent number of inches
            local fracstr = inclean:match('%.(.*)') or ''
            local fmt
            if fracstr == '' then
                fmt = '%.0f'
            else
                fmt = '%.' .. format('%d', #fracstr - 1) .. 'f'
            end
            return true, {
                invalue = inch_value,
                inclean = format(fmt, inch_value),
                outvalue = outvalue,
                minprec = 0,
            }
        end
    end
    return false, { 'cvt_bug_convert' }  -- should never occur
end

local function cvtround(parms, info, in_current, out_current)
    -- Return true, t where t is a table with the conversion results; fields:
    --   show = rounded, formatted string with the result of converting value in info,
    --      using the rounding specified in parms.
    --   singular = true if result is positive, and (after rounding)
    --      is "1", or like "1.00";
    --   (and more fields shown below, and a calculated 'absvalue' field).
    -- or return true, nil if no value specified;
    -- or return false, t where t is an error message table.
    -- Input info.clean uses en digits (it has been translated, if necessary).
    -- Output show uses en or non-en digits as appropriate, or can be spelled.
    local invalue, inclean, show, exponent, singular
    if info then
        invalue, inclean = info.value, info.clean
    end
    if invalue == nil or invalue == '' then
        return true, nil
    end
    if out_current.builtin == 'hand' then
        -- Convert to hands, then convert the fractional part to inches.
        -- Code is not correct when output is spelled, and it ignores any requested
        -- precision if the output uses scientific notation (very large, or very
        -- small). Not worth more complexity as these cases should be very rare.
        local dummy_unit_table = { scale = out_current.scale }
        local success, outinfo = cvtround(parms, info, in_current, dummy_unit_table)
        if not success then return false, outinfo end
        local fmt
        if outinfo.is_scientific then
            fmt = '%.1f'
        else
            local fraction = (outinfo.show):match('[' .. numdot .. '](.*)') or ''  -- outinfo.show is in local language
            if fraction == '' then
                if not outinfo.use_default_precision then
                    return true, outinfo
                end
                fmt = '%.0f'
            else
                fmt = '%.' .. format('%d', ulen(fraction) - 1) .. 'f'
            end
        end
        local hands, inches = math.modf(outinfo.raw_absvalue)
        inches = format(fmt, inches * 4)
        if inches:sub(1, 1) == '4' then
            hands = hands + 1
            inches = '0' .. inches:sub(2)
            if tonumber(inches) == 0 then
                inches = '0'
            end
        end
        if inches:sub(2, 2) == '.' then
            inches = inches:sub(1, 1) .. inches:sub(3)
        end
        return true, {
            sign = outinfo.sign,
            singular = outinfo.singular,
            show = outinfo.sign .. with_separator(parms, format('%d', hands)) .. numdot .. from_en(inches)
        }
    end
    local outvalue, extra = convert(invalue, inclean, in_current, out_current)
    if extra then
        if not outvalue then return false, extra end
        invalue = extra.invalue or invalue
        inclean = extra.inclean or inclean
        outvalue = extra.outvalue
    end
    if not valid_number(outvalue) then
        return false, { 'cvt_invalid_num' }
    end
    local isnegative
    if outvalue < 0 then
        isnegative = true
        outvalue = -outvalue
    end
    local success, use_default_precision
    local precision = parms.precision
    if not precision then
        local sigfig = parms.sigfig
        if sigfig then
            show, exponent = make_sigfig(outvalue, sigfig)
        elseif parms.opt_round5 then
            show = format('%.0f', floor((outvalue / 5) + 0.5) * 5)
        else
            use_default_precision = true
            precision = default_precision(invalue, inclean, outvalue, in_current, out_current, extra)
        end
    end
    if precision then
        if precision >= 0 then
            if precision <= 8 then
                -- Add a fudge to handle common cases of bad rounding due to inability
                -- to precisely represent some values. This makes the following work:
                -- {{convert|-100.1|C|K}} and {{convert|5555000|um|m|2}}.
                -- Old template uses #expr round, which invokes PHP round().
                -- LATER: Investigate how PHP round() works.
                outvalue = outvalue + 2e-14
            end
            local fmt = '%.' .. format('%d', precision) .. 'f'
            local success
            success, show = pcall(format, fmt, outvalue)
            if not success then
                return false, { 'cvt_big_prec', tostring(precision) }
            end
        else
            precision = -precision  -- #digits to zero (in addition to any digits after dot)
            local shift = 10 ^ precision
            show = format('%.0f', outvalue/shift)
            if show ~= '0' then
                exponent = #show + precision
            end
        end
    end
    if (show == '1' or show:match('^1%.0*$') ~= nil) and not isnegative then
        -- Use match because on some systems 0.99999999999999999 is 1.0.
        singular = true
    end
    local t = format_number(parms, show, exponent, isnegative)
    t.singular = singular
    t.raw_absvalue = outvalue  -- absolute value before rounding
    t.use_default_precision = use_default_precision
    return true, setmetatable(t, {
        __index = function (self, key)
            if key == 'absvalue' then
                -- Calculate absolute value after rounding, if needed.
                local clean, exponent = rawget(self, 'clean'), rawget(self, 'exponent')
                local value = tonumber(clean)  -- absolute value (any negative sign has been ignored)
                if exponent then
                    value = value * 10^exponent
                end
                rawset(self, key, value)
                return value
            end
        end })
end

local function evaluate_condition(value, condition)
    -- Return true or false from applying a conditional expression to value,
    -- or throw an error if invalid.
    -- A very limited set of expressions is supported:
    --    v < 9
    --    v * 9 < 9
    -- where
    --    'v' is replaced with value
    --    9 is any number (as defined by Lua tonumber)
    --      only en digits are accepted
    --    '<' can also be '<=' or '>' or '>='
    -- In addition, the following form is supported:
    --    LHS and RHS
    -- where
    --    LHS, RHS = any of above expressions.
    local function compare(value, text)
        local arithop, factor, compop, limit = text:match('^%s*v%s*([*]?)(.-)([<>]=?)(.*)$')
        if arithop == nil then
            error('Invalid default expression', 0)
        elseif arithop == '*' then
            factor = tonumber(factor)
            if factor == nil then
                error('Invalid default expression', 0)
            end
            value = value * factor
        end
        limit = tonumber(limit)
        if limit == nil then
            error('Invalid default expression', 0)
        end
        if compop == '<' then
            return value < limit
        elseif compop == '<=' then
            return value <= limit
        elseif compop == '>' then
            return value > limit
        elseif compop == '>=' then
            return value >= limit
        end
        error('Invalid default expression', 0)  -- should not occur
    end
    local lhs, rhs = condition:match('^(.-%W)and(%W.*)')
    if lhs == nil then
        return compare(value, condition)
    end
    return compare(value, lhs) and compare(value, rhs)
end

local function get_default(value, unit_table)
    -- Return true, s where s = name of unit's default output unit,
    -- or return false, t where t is an error message table.
    -- Some units have a default that depends on the input value
    -- (the first value if a range of values is used).
    -- If '!' is in the default, the first bang-delimited field is an
    -- expression that uses 'v' to represent the input value.
    -- Example: 'v < 120 ! small ! big ! suffix' (suffix is optional)
    -- evaluates 'v < 120' as a boolean with result
    -- 'smallsuffix' if (value < 120), or 'bigsuffix' otherwise.
    -- Input must use en digits and '.' decimal mark.
    local default = default_exceptions[unit_table.defkey or unit_table.symbol] or unit_table.default
    if default == nil then
        return false, { 'cvt_no_default', unit_table.symbol }
    end
    if default:find('!', 1, true) == nil then
        return true, default
    end
    local t = split(default, '!')
    if #t == 3 or #t == 4 then
        local success, result = pcall(evaluate_condition, value, t[1])
        if success then
            default = result and t[2] or t[3]
            if #t == 4 then
                default = default .. t[4]
            end
            return true, default
        end
    end
    return false, { 'cvt_bad_default', unit_table.symbol }
end

local linked_pages  -- to record linked pages so will not link to the same page more than once

local function make_link(link, id, link_key)
    -- Return wikilink "[[link|id]]", possibly abbreviated as in examples:
    --   [[Mile|mile]]  --> [[mile]]
    --   [[Mile|miles]] --> [[mile]]s
    -- However, just id is returned if:
    -- * no link given (so caller does not need to check if a link was defined); or
    -- * link has previously been used during the current convert (to avoid overlinking).
    -- Linking with a unit uses the unit table as the link key, which fails to detect
    -- overlinking for conversions like (each links "mile" twice):
    --   {{convert|1|impgal/mi|USgal/mi|lk=on}}
    --   {{convert|1|l/km|impgal/mi USgal/mi|lk=on}}
    link_key = link_key or link  -- use key if given (the key, but not the link, may be known when need to cancel a link record)
    if link == nil or link == '' or linked_pages[link_key] then
        return id
    end
    linked_pages[link_key] = true
    -- Following only works for language en, but it should be safe on other wikis,
    -- and overhead of doing it generally does not seem worthwhile.
    local l = link:sub(1, 1):lower() .. link:sub(2)
    if link == id or l == id then
        return '[[' .. id .. ']]'
    elseif link .. 's' == id or l .. 's' == id then
        return '[[' .. id:sub(1, -2) .. ']]s'
    else
        return '[[' .. link .. '|' .. id .. ']]'
    end
end

local function linked_id(unit_table, key_id, want_link)
    -- Return final unit id (symbol or name), optionally with a wikilink,
    -- and update unit_table.sep if required.
    -- key_id is one of: 'symbol', 'sym_us', 'name1', 'name1_us', 'name2', 'name2_us'.
    local abbr_on = (key_id == 'symbol' or key_id == 'sym_us')
    if abbr_on and want_link then
        local symlink = rawget(unit_table, 'symlink')
        if symlink then
            return symlink  -- for exceptions that have the linked symbol built-in
        end
    end
    local multiplier = rawget(unit_table, 'multiplier')
    local per = unit_table.per
    if per then
        local unit1 = per[1]  -- top unit_table, or nil
        local unit2 = per[2]  -- bottom unit_table
        if abbr_on then
            if not unit1 then
                unit_table.sep = ''  -- no separator in "$2/acre"
            end
            if not want_link then
                local symbol = unit_table.symbol_raw
                if symbol then
                    return symbol  -- for exceptions that have the symbol built-in
                end
            end
        end
        local key_id2  -- unit2 is always singular
        if key_id == 'name2' then
            key_id2 = 'name1'
        elseif key_id == 'name2_us' then
            key_id2 = 'name1_us'
        else
            key_id2 = key_id
        end
        local result
        if abbr_on then
            result = '/'
        elseif unit1 then
            result = ' per '
        else
            result = 'per '
        end
        if unit1 then
            result = linked_id(unit1, key_id, want_link) .. result
        end
        return result .. linked_id(unit2, key_id2, want_link)
    end
    if multiplier then
        -- A multiplier (like "100" in "100km") forces the unit to be plural.
        if abbr_on then
            multiplier = multiplier .. '&nbsp;'
        else
            multiplier = multiplier .. ' '
            if key_id == 'name1' then
                key_id = 'name2'
            elseif key_id == 'name1_us' then
                key_id = 'name2_us'
            end
        end
    else
        multiplier = ''
    end
    local id = unit_table.fixed_name or unit_table[key_id]
    if want_link then
        local link = link_exceptions[unit_table.symbol] or unit_table.link
        if link then
            local before = ''
            local i = unit_table.customary
            if i == 1 and unit_table.sp_us then
                i = 2  -- show "U.S." not "US"
            end
            if i == 3 and abbr_on then
                i = 4  -- abbreviate "imperial" to "imp"
            end
            local customary = customary_units[i]
            if customary then
                -- LATER: This works for language en only, but it's esoteric so ignore for now.
                local pertext
                if id:sub(1, 1) == '/' then
                    -- Want unit "/USgal" to display as "/U.S. gal", not "U.S. /gal".
                    pertext = '/'
                    id = id:sub(2)
                elseif id:sub(1, 4) == 'per ' then
                    -- Similarly want "per U.S. gallon", not "U.S. per gallon" (but in practice this is unlikely to be used).
                    pertext = 'per '
                    id = id:sub(5)
                else
                    pertext = ''
                end
                -- Omit any "US"/"U.S."/"imp"/"imperial" from start of id since that will be inserted.
                local removes = (i < 3) and { 'US&nbsp;', 'US ', 'U.S.&nbsp;', 'U.S. ' } or { 'imp&nbsp;', 'imp ', 'imperial ' }
                for _, prefix in ipairs(removes) do
                    local plen = #prefix
                    if id:sub(1, plen) == prefix then
                        id = id:sub(plen + 1)
                        break
                    end
                end
                before = pertext .. make_link(customary.link, customary[1]) .. ' '
            end
            id = before .. make_link(link, id, unit_table)
        end
    end
    return multiplier .. id
end

local function make_id(parms, which, unit_table)
    -- Return id, f where
    --   id = unit name or symbol, possibly modified
    --   f = true if id is a name, or false if id is a symbol
    -- using 1st or 2nd values (which), and for 'in' or 'out' (unit_table.inout).
    -- Result is '' if no symbol/name is to be used.
    -- In addition, set unit_table.sep = ' ' or '&nbsp;' or ''
    -- (the separator that caller will normally insert before the id).
    if parms.opt_values then
        unit_table.sep = ''
        return ''
    end
    local inout = unit_table.inout
    local valinfo = unit_table.valinfo
    local abbr_org = parms.abbr_org
    local adjectival = parms.opt_adjectival
    local disp = parms.disp
    local lk = parms.lk
    local usename = unit_table.usename
    local singular = valinfo[which].singular
    if usename then
        -- Old template does something like this.
        if lk == 'on' or lk == inout then
            -- A linked unit uses the standard singular.
        else
            -- Set non-standard singular.
            local flipped = parms.opt_flip
            if inout == 'in' then
                if not adjectival and (abbr_org == 'out' or flipped) then
                    local value = valinfo[which].value
                    singular = (0 < value and value < 1.0001)
                end
            else
                if (abbr_org == 'on') or
                (not flipped and (abbr_org == nil or abbr_org == 'out')) or
                (flipped and abbr_org == 'in') then
                    singular = (valinfo[which].absvalue < 1.0001 and
                                not valinfo[which].is_scientific)
                end
            end
        end
    end
    local want_name
    if usename then
        want_name = true
    else
        if abbr_org == nil then
            if disp == 'br' or disp == 'or' or disp == 'slash' then
                want_name = true
            end
            if unit_table.utype == 'temperature' or unit_table.utype == 'temperature change' then
                if not (unit_table.exception == 'temperature') then
                    want_name = false
                end
            end
        end
        if want_name == nil then
            local abbr = parms.abbr
            if abbr == 'on' or abbr == inout or (abbr == 'mos' and inout == 'out') then
                want_name = false
            else
                want_name = true
            end
        end
    end
    local key
    if want_name then
        if parms.opt_use_nbsp then
            unit_table.sep = '&nbsp;'
        else
            unit_table.sep = ' '
        end
        if parms.opt_singular then
            local value
            if inout == 'in' then
                value = valinfo[which].value
            else
                value = valinfo[which].absvalue
            end
            if value then  -- some unusual units do not always set value field
                value = abs(value)
                singular = (0 < value and value < 1.0001)
            end
        end
        if unit_table.engscale or parms.is_range_x then
            -- engscale: so "|1|e3kg" gives "1 thousand kilograms" (plural)
            -- is_range_x: so "|0.5|x|0.9|mi" gives "0.5 by 0.9 miles" (plural)
            singular = false
        end
        key = (adjectival or singular) and 'name1' or 'name2'
        if unit_table.sp_us then
            key = key .. '_us'
        end
    else
        unit_table.sep = '&nbsp;'
        key = unit_table.sp_us and 'sym_us' or 'symbol'
    end
    return linked_id(unit_table, key, lk == 'on' or lk == inout), want_name
end

local function decorate_value(parms, unit_table, which)
    -- If needed, update unit_table so values will be shown with extra information.
    -- For consistency with the old template (but different from fmtpower),
    -- the style to display powers of 10 includes "display:none" to allow some
    -- browsers to copy, for example, "10³" as "10^3", rather than as "103".
    local engscale = unit_table.engscale
    if engscale then
        local inout = unit_table.inout
        local info = unit_table.valinfo[which]
        local abbr = parms.abbr
        if abbr == 'on' or abbr == inout then
            info.show = info.show ..
                '<span style="margin-left:0.2em">×<span style="margin-left:0.1em">' ..
                from_en('10') ..
                '</span></span><s style="display:none">^</s><sup>' ..
                from_en(tostring(engscale.exponent)) .. '</sup>'
        else
            local number_id
            local lk = parms.lk
            if lk == 'on' or lk == inout then
                number_id = make_link(engscale.link, engscale[1])
            else
                number_id = engscale[1]
            end
            -- WP:NUMERAL recommends "&nbsp;" in values like "12 million".
            info.show = info.show .. (parms.opt_adjectival and '-' or '&nbsp;') .. number_id
        end
    end
    local prefix = unit_table.vprefix
    if prefix then
        local info = unit_table.valinfo[which]
        info.show = prefix .. info.show
    end
end

local function process_input(parms, in_current)
    -- Processing required once per conversion.
    -- Return block of text to represent input (value/unit).
    if parms.opt_output_only or parms.opt_output_number_only or parms.opt_output_unit_only then
        parms.joins = { '', '' }
        return ''
    end
    local first_unit
    local composite = in_current.composite  -- nil or table of units
    if composite then
        first_unit = composite[1]
    else
        first_unit = in_current
    end
    local id1, want_name = make_id(parms, 1, first_unit)
    local sep = first_unit.sep  -- separator between value and unit, set by make_id
    local preunit = parms.preunit1
    if preunit then
        sep = ''  -- any separator is included in preunit
    else
        preunit = ''
    end
    if parms.opt_input_unit_only then
        parms.joins = { '', '' }
        if composite then
            local parts = { id1 }
            for i, unit in ipairs(composite) do
                if i > 1 then
                    table.insert(parts, (make_id(parms, 1, unit)))
                end
            end
            id1 = table.concat(parts, ' ')
        end
        if want_name and parms.opt_adjectival then
            return preunit .. hyphenated(id1)
        end
        return  preunit .. id1
    end
    local abbr = parms.abbr
    local disp = parms.disp
    if disp == nil then  -- special case for the most common setting
        parms.joins = disp_joins['b']
    elseif disp ~= 'x' then
        -- Old template does this.
        if disp == 'slash' then
            if parms.abbr_org == nil then
                disp = 'slash-nbsp'
            elseif abbr == 'in' or abbr == 'out' then
                disp = 'slash-sp'
            else
                disp = 'slash-nosp'
            end
        elseif disp == 'sqbr' then
            if abbr == 'on' then
                disp = 'sqbr-nbsp'
            else
                disp = 'sqbr-sp'
            end
        end
        parms.joins = disp_joins[disp] or disp_joins['b']
    end
    if parms.opt_also_symbol and not composite then
        local join1 = parms.joins[1]
        if join1 == ' (' or join1 == ' [' then
            parms.joins = { join1 .. first_unit[first_unit.sp_us and 'sym_us' or 'symbol'] .. ', ', parms.joins[2] }
        end
    end
    if in_current.builtin == 'mach' then
        local prefix = id1 .. '&nbsp;'
        local range = parms.range
        local valinfo = first_unit.valinfo
        local result = prefix .. valinfo[1].show
        if range then
            -- For simplicity and because more not needed, handle one range item only.
            local prefix2 = make_id(parms, 2, first_unit) .. '&nbsp;'
            result = range_text(range[1], want_name, parms, result, prefix2 .. valinfo[2].show)
        end
        return preunit .. result
    end
    if composite then
        -- Simplify: assume there is no range, and no decoration.
        local mid = ''
        local sep1 = '&nbsp;'
        local sep2 = ' '
        if parms.opt_adjectival then
            if not parms.opt_flip then
                mid = parms.mid or ''
            end
            if want_name then
                sep1 = '-'
                sep2 = '-'
            end
        end
        local parts = { first_unit.valinfo[1].show .. sep1 .. id1 }
        for i, unit in ipairs(composite) do
            if i > 1 then
                table.insert(parts, unit.valinfo[1].show .. sep1 .. (make_id(parms, 1, unit)))
            end
        end
        return table.concat(parts, sep2) .. mid
    end
    local result, mos
    local range = parms.range
    if range then
        mos = (abbr == 'mos')
        if not (mos or (parms.is_range_x and not want_name)) then
            linked_pages[first_unit] = nil  -- so the second and only id will be linked, if wanted
        end
    end
    local id = (range == nil) and id1 or make_id(parms, 2, first_unit)
    local extra, was_hyphenated = hyphenated_maybe(parms, want_name, sep, id, 'in')
    if mos and was_hyphenated then
        mos = false  -- suppress repeat of unit in a range
        if linked_pages[first_unit] then
            linked_pages[first_unit] = nil
            id = make_id(parms, 2, first_unit)
            extra = hyphenated_maybe(parms, want_name, sep, id, 'in')
        end
    end
    local valinfo = first_unit.valinfo
    if range then
        if range.n == 1 then
            -- Like {{convert|1|x|2|ft}} (one range item; two values).
            -- Do what old template did.
            local sep1 = first_unit.sep
            if mos then
                decorate_value(parms, in_current, 1)
                decorate_value(parms, in_current, 2)
                result = valinfo[1].show .. sep1 .. id1
            elseif parms.is_range_x and not want_name then
                if abbr == 'in' or abbr == 'on' then
                    decorate_value(parms, in_current, 1)
                end
                decorate_value(parms, in_current, 2)
                result = valinfo[1].show .. sep1 .. id1
            else
                if abbr == 'in' or abbr == 'on' then
                    decorate_value(parms, in_current, 1)
                end
                decorate_value(parms, in_current, 2)
                result = valinfo[1].show
            end
            result = range_text(range[1], want_name, parms, result, valinfo[2].show)
        else
            -- Like {{convert|1|x|2|x|3|ft}} (two or more range items): simplify.
            decorate_value(parms, in_current, 1)
            result = valinfo[1].show
            for i = 1, range.n do
                decorate_value(parms, in_current, i+1)
                result = range_text(range[i], want_name, parms, result, valinfo[i+1].show)
            end
        end
    else
        decorate_value(parms, first_unit, 1)
        result = valinfo[1].show
    end
    return result .. preunit .. extra
end

local function process_one_output(parms, out_current)
    -- Processing required for each output unit.
    -- Return block of text to represent output (value/unit).
    local id1, want_name = make_id(parms, 1, out_current)
    local sep = out_current.sep  -- set by make_id
    local preunit = parms.preunit2
    if preunit then
        sep = ''  -- any separator is included in preunit
    else
        preunit = ''
    end
    if parms.opt_output_unit_only then
        if want_name and parms.opt_adjectival then
            return preunit .. hyphenated(id1)
        end
        return preunit .. id1
    end
    if out_current.builtin == 'mach' then
        local prefix = id1 .. '&nbsp;'
        local range = parms.range
        local valinfo = out_current.valinfo
        local result = prefix .. valinfo[1].show
        if range then
            -- For simplicity and because more not needed, handle one range item only.
            result = range_text(range[1], want_name, parms, result, prefix .. valinfo[2].show)
        end
        return preunit .. result
    end
    local result
    local range = parms.range
    if range then
        if not (parms.is_range_x and not want_name) then
            linked_pages[out_current] = nil  -- so the second and only id will be linked, if wanted
        end
    end
    local id = (range == nil) and id1 or make_id(parms, 2, out_current)
    local extra = hyphenated_maybe(parms, want_name, sep, id, 'out')
    local valinfo = out_current.valinfo
    if range then
        if range.n == 1 then
            local sep1 = out_current.sep
            local abbr = parms.abbr
            if parms.is_range_x and not want_name then
                if abbr == 'out' or abbr == 'on' then
                    decorate_value(parms, out_current, 1)
                end
                decorate_value(parms, out_current, 2)
                result = valinfo[1].show .. sep1 .. id1
            else
                if abbr == 'out' or abbr == 'on' then
                    decorate_value(parms, out_current, 1)
                end
                decorate_value(parms, out_current, 2)
                result = valinfo[1].show
            end
            result = range_text(range[1], want_name, parms, result, valinfo[2].show)
        else
            -- Like {{convert|1|x|2|x|3|ft}} (two or more range items): simplify.
            decorate_value(parms, out_current, 1)
            result = valinfo[1].show
            for i = 1, range.n do
                decorate_value(parms, out_current, i+1)
                result = range_text(range[i], want_name, parms, result, valinfo[i+1].show)
            end
        end
    else
        decorate_value(parms, out_current, 1)
        result = valinfo[1].show
    end
    if parms.opt_output_number_only then
        return result
    end
    return result .. preunit .. extra
end

local function make_output_single(parms, in_unit_table, out_unit_table)
    -- Return true, item where item = wikitext of the conversion result
    -- for a single output (which is not a combination or a multiple);
    -- or return false, t where t is an error message table.
    out_unit_table.valinfo = collection()
    local range = parms.range
    for i = 1, (range and (range.n + 1) or 1) do
        local success, info = cvtround(parms, in_unit_table.valinfo[i], in_unit_table, out_unit_table)
        if not success then return false, info end
        out_unit_table.valinfo:add(info)
    end
    return true, process_one_output(parms, out_unit_table)
end

local function make_output_multiple(parms, in_unit_table, out_unit_table)
    -- Return true, item where item = wikitext of the conversion result
    -- for an output which is a multiple (like 'ftin');
    -- or return false, t where t is an error message table.
    local multiple = out_unit_table.multiple  -- table of scaling factors (will not be nil)
    local combos = out_unit_table.combination  -- table of unit tables (will not be nil)
    local abbr = parms.abbr
    local abbr_org = parms.abbr_org
    local disp = parms.disp
    local want_name = (abbr_org == nil and (disp == 'or' or disp == 'slash')) or
                      not (abbr == 'on' or abbr == 'out' or abbr == 'mos')
    local want_link = (parms.lk == 'on' or parms.lk == 'out')
    local mid = ''
    local sep1 = '&nbsp;'
    local sep2 = ' '
    if parms.opt_adjectival then
        if parms.opt_flip then
            mid = parms.mid or ''
        end
        if want_name then
            sep1 = '-'
            sep2 = '-'
        end
    end
    local function make_result(info)
        local fmt, outvalue, sign
        local results = {}
        for i = 1, #combos do
            local thisvalue, strforce
            local out_current = combos[i]
            out_current.inout = 'out'
            local scale = multiple[i]
            if i == 1 then  -- least significant unit ('in' from 'ftin')
                local fraction
                local success, outinfo = cvtround(parms, info, in_unit_table, out_current)
                if not success then return false, outinfo end
                sign = outinfo.sign
                if outinfo.is_scientific then
                    strforce = outinfo.show
                    fraction = ''
                else
                    fraction = (outinfo.show):match('[' .. numdot .. '](.*)') or ''  -- outinfo.show is in local language
                end
                fmt = '%.' .. ulen(fraction) .. 'f'  -- to reproduce precision
                if fraction == '' then
                    outvalue = floor(outinfo.raw_absvalue + 0.5)  -- keep all integer digits of least significant unit
                else
                    outvalue = outinfo.absvalue
                end
            end
            if scale then
                outvalue, thisvalue = floor(outvalue / scale), outvalue % scale
            else
                thisvalue = outvalue
            end
            local id
            if want_name then
                id = out_current[(thisvalue == 1) and 'name1' or 'name2']
            else
                id = out_current['symbol']
            end
            if want_link then
                local link = out_current.link
                if link then
                    id = make_link(link, id, out_current)
                end
            end
            local strval
            if strforce and outvalue == 0 then
                sign = ''  -- any sign is in strforce
                strval = strforce  -- show small values in scientific notation; will only use least significant unit
            else
                strval = (thisvalue == 0) and from_en('0') or with_separator(parms, format(fmt, thisvalue))
            end
            table.insert(results, strval .. sep1 .. id)
            if outvalue == 0 then
                break
            end
            fmt = '%.0f'  -- only least significant unit can have a fraction
        end
        local reversed, count = {}, #results
        for i = 1, count do
            reversed[i] = results[count + 1 - i]
        end
        return true, sign .. table.concat(reversed, sep2)
    end
    local valinfo = in_unit_table.valinfo
    local success, result = make_result(valinfo[1])
    if not success then return false, result end
    local range = parms.range
    if range then
        for i = 1, range.n do
            local success, result2 = make_result(valinfo[i+1])
            if not success then return false, result2 end
            result = range_text(range[i], want_name, parms, result, result2)
        end
    end
    return true, result .. mid
end

local function process(parms, in_unit_table)
    -- Return true, s where s = final wikitext result,
    -- or return false, t where t is an error message table.
    linked_pages = {}
    local success, out_unit_table
    local invalue1 = in_unit_table.valinfo[1].value
    local out_unit = parms.out_unit
    if out_unit == nil or out_unit == '' then
        success, out_unit = get_default(invalue1, in_unit_table)
        if not success then return false, out_unit end
    end
    success, out_unit_table = lookup(out_unit, parms.opt_sp_us, 'any_combination')
    if not success then return false, out_unit_table end
    if in_unit_table.utype ~= out_unit_table.utype then
        return false, { 'cvt_mismatch', in_unit_table.utype, out_unit_table.utype }
    end
    local flipped = parms.opt_flip
    local parts = {}
    for part = 1, 2 do
        -- The LHS (parts[1]) is normally the input, but is the output if flipped.
        -- Process LHS first so it will be linked, if wanted.
        -- Linking to the same item is suppressed in the RHS to avoid overlinking.
        if (part == 1 and not flipped) or (part == 2 and flipped) then
            parts[part] = process_input(parms, in_unit_table)
        else
            local outputs = {}
            local combos  -- nil (for 'ft' or 'ftin'), or table of unit tables (for 'm ft')
            if out_unit_table.multiple == nil then  -- nil ('ft' or 'm ft'), or table of factors ('ftin')
                combos = out_unit_table.combination
            end
            local imax = combos and #combos or 1  -- 1 (single unit) or number of unit tables
            for i = 1, imax do
                local success, item
                local out_current = combos and combos[i] or out_unit_table
                out_current.inout = 'out'
                if out_current.multiple == nil then
                    success, item = make_output_single(parms, in_unit_table, out_current)
                else
                    success, item = make_output_multiple(parms, in_unit_table, out_current)
                end
                if not success then return false, item end
                table.insert(outputs, item)
            end
            parts[part] = parms.opt_input_unit_only and '' or table.concat(outputs, '; ')
        end
    end
    if parms.opt_sortable then
        parts[1] = ntsh(invalue1, parms.opt_sortable_debug) .. parts[1]
    end
    local wikitext
    if parms.table_joins then
        wikitext = parms.table_joins[1] .. parts[1] .. parms.table_joins[2] .. parts[2]
    else
        wikitext = parts[1] .. parms.joins[1] .. parts[2] .. parms.joins[2]
    end
    if parms.warnings then
        wikitext = wikitext .. parms.warnings
    end
    return true, wikitext
end

local function main_convert(frame)
    set_config(frame)
    local result
    local success, parms, in_unit_table = get_parms(frame:getParent())
    if success then
        success, result = process(parms, in_unit_table)
    else
        result = parms
    end
    if success then
        return result
    end
    return message(result)
end

return { convert = main_convert }