if not modules then modules = { } end modules ['math-fbk'] = {
    version   = 1.001,
    comment   = "companion to math-ini.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

-- This will partly be redone and go via definitions in goodies where we can share
-- some across fonts. That makes most sense for those patches that might need some
-- finetuning depending on the font.

local next, type = next, type

local trace_fallbacks   = false  trackers.register("math.fallbacks", function(v) trace_fallbacks = v end)

local report_fallbacks  = logs.reporter("math","fallbacks")

local formatters        = string.formatters
local fastcopy          = table.fastcopy
local byte              = string.byte
local sortedhash        = table.sortedhash
local setmetatableindex = table.setmetatableindex

local fallbacks         = { }
mathematics.fallbacks   = fallbacks

----- helpers           = fonts.helpers
----- charcommand       = helpers.commands.char
----- slotcommand       = helpers.commands.slot
----- leftcommand       = helpers.commands.left
----- rightcommand      = helpers.commands.right
----- upcommand         = helpers.commands.up
----- downcommand       = helpers.commands.down
----- popcommand        = helpers.commands.pop
----- pushcommand       = helpers.commands.push

local virtualcharacters = { }
local virtualforced     = { }

local hashes            = fonts.hashes
local identifiers       = hashes.identifiers
local lastmathids       = hashes.lastmathids

-- we need a trick (todo): if we define scriptscript, script and text in
-- that order we could use their id's .. i.e. we could always add a font
-- table with those id's .. in fact, we could also add a whole lot more
-- as it doesn't hurt

function fallbacks.apply(target,original)
    local mathparameters = target.mathparameters
    if not mathparameters or not next(mathparameters) then
        return
    end
    -- we also have forcedsize ... at this moment we already passed through
    -- constructors.scale so we have this set
    local parameters = target.parameters
    local properties = target.properties
    local mathsize   = parameters.mathsize
    if mathsize < 1 or mathsize > 3 then
        return
    end
    local characters  = target.characters
    local size        = parameters.size
    local usedfonts   = target.fonts
    local compactmath = properties.compactmath
    if not usedfonts then
        usedfonts    = { { id = 0 } } -- we need at least one entry (automatically done anyway)
        target.fonts = usedfonts
    end
    -- not used
    local textid, scriptid, scriptscriptid
    local textindex, scriptindex, scriptscriptindex
    local textdata, scriptdata, scriptscriptdata
    if mathsize == 3 then
        -- scriptscriptsize
        textid         = 0
        scriptid       = 0
        scriptscriptid = 0
    elseif mathsize == 2 then
        -- scriptsize
        textid         = 0
        scriptid       = lastmathids[3] or 0
        scriptscriptid = lastmathids[3] or 0
    else
        -- textsize
        textid         = 0
        scriptid       = lastmathids[2] or 0
        scriptscriptid = lastmathids[3] or 0
    end
    if textid and textid ~= 0 then
        textindex = #usedfonts + 1
        textdata  = target
        usedfonts[textindex] = { id = textid }
    else
        textdata = target
    end
    if compactmath then
        scriptid       = textid
        scriptscriptid = textid
    end
    if scriptid and scriptid ~= 0 then
        scriptindex = #usedfonts  + 1
        scriptdata  = identifiers[scriptid]
        usedfonts[scriptindex] = { id = scriptid }
    else
        scriptindex = textindex
        scriptdata  = textdata
    end
    if scriptscriptid and scriptscriptid ~= 0 then
        scriptscriptindex = #usedfonts  + 1
        scriptscriptdata  = identifiers[scriptscriptid]
        usedfonts[scriptscriptindex] = { id = scriptscriptid }
    else
        scriptscriptindex = scriptindex
        scriptscriptdata  = scriptdata
    end
    -- report_fallbacks("used textid: %S, used script id: %S, used scriptscript id: %S",textid,scriptid,scriptscriptid)
    local data = {
        textdata          = textdata,
        scriptdata        = scriptdata,
        scriptscriptdata  = scriptscriptdata,
        textindex         = textindex,
        scriptindex       = scriptindex,
        scriptscriptindex = scriptscriptindex,
        textid            = textid,
        scriptid          = scriptid,
        scriptscriptid    = scriptscriptid,
        characters        = characters,
        unicode           = k,
        target            = target,
        original          = original,
        size              = size,
        mathsize          = mathsize,
    }
    target.mathrelation = data
    --
    local fullname = trace_fallbacks and target.properties.fullname
    --
    for k, v in sortedhash(virtualcharacters) do
        if not characters[k] or virtualforced[k] then
            local tv = type(v)
            local cd = nil
            if tv == "table" then
                cd = v
            elseif tv == "number" then
                cd = characters[v]
            elseif tv == "function" then
                cd = v(data) -- ,k
            end
            if cd then
                characters[k] = cd
            else
                -- something else
            end
            if trace_fallbacks and characters[k] then
                report_fallbacks("extending math font %a with %U",fullname,k)
            end
        end
    end
    data.unicode = nil
end

utilities.sequencers.appendaction("aftercopyingcharacters","system","mathematics.fallbacks.apply")

function fallbacks.install(unicode,value)
    virtualcharacters[unicode] = value
end

-- a few examples:

-- local addextra = mathematics.extras.add

-- addextra(0xFE350) -- MATHEMATICAL DOUBLE ARROW LEFT END
-- addextra(0xFE351) -- MATHEMATICAL DOUBLE ARROW MIDDLE PART
-- addextra(0xFE352) -- MATHEMATICAL DOUBLE ARROW RIGHT END
--
-- local leftarrow  = charcommand[0x2190]
-- local relbar     = charcommand[0x2212]
-- local rightarrow = charcommand[0x2192]
--
-- virtualcharacters[0xFE350] = function(data)
--  -- return combined(data,0x2190,0x2212) -- leftarrow relbar
--     local charone = data.characters[0x2190]
--     local chartwo = data.characters[0x2212]
--     if charone and chartwo then
--         local size = data.size/2
--         return {
--             width    = chartwo.width,
--             height   = size,
--             depth    = size,
--             commands = {
--                 pushcommand,
--                 downcommand[size/2],
--                 leftarrow,
--                 popcommand,
--                 upcommand[size/2],
--                 relbar,
--             }
--         }
--     end
-- end
--
-- virtualcharacters[0xFE351] = function(data)
--  -- return combined(data,0x2212,0x2212) -- relbar, relbar  (isn't that just equal)
--     local char = data.characters[0x2212]
--     if char then
--         local size = data.size/2
--         return {
--             width    = char.width,
--             height   = size,
--             depth    = size,
--             commands = {
--                 pushcommand,
--                 downcommand[size/2],
--                 relbar,
--                 popcommand,
--                 upcommand[size/2],
--                 relbar,
--             }
--         }
--     end
-- end
--
-- virtualcharacters[0xFE352] = function(data)
--  -- return combined(data,0x2192,0x2212) -- rightarrow relbar
--     local charone = data.characters[0x2192]
--     local chartwo = data.characters[0x2212]
--     if charone and chartwo then
--         local size = data.size/2
--         return {
--             width    = chartwo.width,
--             height   = size,
--             depth    = size,
--             commands = {
--                 pushcommand,
--                 downcommand[size/2],
--                 relbar,
--                 popcommand,
--                 rightcommand[chartwo.width - charone.width],
--                 upcommand[size/2],
--                 rightarrow,
--             }
--         }
--     end
-- end

---------------------------------------------------------------------------------
-- these are moved to math-act.lmt (keep this code)
---------------------------------------------------------------------------------

-- local function accent_to_extensible(target,newchr,original,oldchr,height,depth,swap,offset,unicode)
--     local characters = target.characters
--     local olddata = characters[oldchr]
--     -- brrr ... pagella has only next
--     if olddata and not olddata.commands then -- not: and olddata.width > 0
--         local addprivate = fonts.helpers.addprivate
--         if swap then
--             swap   = characters[swap]
--             height = swap.depth or 0
--             depth  = 0
--         else
--             height = height or 0
--             depth  = depth  or 0
--         end
--         local oldheight  = olddata.height or 0
--         local correction = swap and
--             downcommand[oldheight - height]
--          or downcommand[oldheight + (offset or 0)]
--         local newdata = {
--             commands = { correction, charcommand[oldchr] },
--             width    = olddata.width,
--             height   = height,
--             depth    = depth,
--             unicode  = unicode,
--         }
--         local glyphdata = newdata
--         local nextglyph = olddata.next
--         while nextglyph do
--             local oldnextdata = characters[nextglyph]
--             if oldnextdata then
--                 local newnextdata = {
--                     commands = { correction, charcommand[nextglyph] },
--                     width    = oldnextdata.width,
--                     height   = height,
--                     depth    = depth,
--                 }
--                 local newnextglyph = addprivate(target,formatters["M-N-%H"](nextglyph),newnextdata)
--                 newdata.next = newnextglyph
--                 local nextnextglyph = oldnextdata.next
--                 if nextnextglyph == nextglyph then
--                     break
--                 else
--                     olddata   = oldnextdata
--                     newdata   = newnextdata
--                     nextglyph = nextnextglyph
--                 end
--             else
--                 report_fallbacks("error in fallback: no valid next, slot %X",nextglyph)
--                 break
--             end
--         end
--         local hv = olddata.hparts
--         if hv then
--             hv = fastcopy(hv)
--             newdata.hparts = hv
--             for i=1,#hv do
--                 local hvi = hv[i]
--                 local oldglyph = hvi.glyph
--                 local olddata = characters[oldglyph]
--                 if olddata then
--                     local newdata = {
--                         commands = { correction, charcommand[oldglyph] },
--                         width    = olddata.width,
--                         height   = height,
--                         depth    = depth,
--                     }
--                     hvi.glyph = addprivate(target,formatters["M-H-%H"](oldglyph),newdata)
--                 else
--                     report_fallbacks("error in fallback: no valid hparts, slot %X, index %i",oldglyph,i)
--                 end
--             end
--         end
--         return glyphdata, true
--     else
--         return olddata, false
--     end
-- end
--
-- virtualcharacters[0x203E] = function(data) -- overbar
--     local target = data.target
--     local height = 0
--     local depth  = 0
--  -- local mathparameters = target.mathparameters
--  -- if mathparameters then
--  --     height = mathparameters.OverbarVerticalGap
--  --     depth  = mathparameters.UnderbarVerticalGap
--  -- else
--         height = target.parameters.xheight/4
--         depth  = height
--  -- end
--     return accent_to_extensible(target,0x203E,data.original,0x0305,height,depth,nil,nil,0x203E)
-- end
--
-- -- virtualcharacters[0xFE33E] = virtualcharacters[0x203E] -- convenient
-- -- virtualcharacters[0xFE33F] = virtualcharacters[0x203E] -- convenient
--
-- virtualcharacters[0xFE33E] = function(data)
--     local target = data.target
--     local height = 0
--     local depth  = target.parameters.xheight/4
--     return accent_to_extensible(target,0xFE33E,data.original,0x0305,height,depth,nil,nil,0x203E)
-- end
--
-- virtualcharacters[0xFE33F] = function(data)
--     local target = data.target
--     local height = target.parameters.xheight/8
--     local depth  = height
--     return accent_to_extensible(target,0xFE33F,data.original,0x0305,height,depth,nil,nil,0x203E)
-- end
--
-- local function smashed(data,unicode,swap,private)
--     local target   = data.target
--     local original = data.original
--     local chardata = target.characters[unicode]
--     if chardata and chardata.height > target.parameters.xheight then
--         return accent_to_extensible(target,private,original,unicode,0,0,swap,nil,unicode)
--     else
--         return original.characters[unicode]
--     end
-- end
--
-- addextra(0xFE3DE) -- EXTENSIBLE OF 0x03DE : overbrace
-- addextra(0xFE3DC) -- EXTENSIBLE OF 0x03DC : overparent
-- addextra(0xFE3B4) -- EXTENSIBLE OF 0x03B4 : overbracket
--
-- virtualcharacters[0xFE3DE] = function(data) return smashed(data,0x23DE,0x23DF,0xFE3DE) end
-- virtualcharacters[0xFE3DC] = function(data) return smashed(data,0x23DC,0x23DD,0xFE3DC) end
-- virtualcharacters[0xFE3B4] = function(data) return smashed(data,0x23B4,0x23B5,0xFE3B4) end
--
-- addextra(0xFE3DF) -- EXTENSIBLE OF 0x03DF
-- addextra(0xFE3DD) -- EXTENSIBLE OF 0x03DD
-- addextra(0xFE3B5) -- EXTENSIBLE OF 0x03B5
--
-- virtualcharacters[0xFE3DF] = function(data) local c = data.target.characters[0x23DF] if c then c.unicode = 0x23DF return c end end
-- virtualcharacters[0xFE3DD] = function(data) local c = data.target.characters[0x23DD] if c then c.unicode = 0x23DD return c end end
-- virtualcharacters[0xFE3B5] = function(data) local c = data.target.characters[0x23B5] if c then c.unicode = 0x23B5 return c end end
--
-- -- todo: add some more .. numbers might change
--
-- addextra(0xFE302) -- EXTENSIBLE OF 0x0302
-- addextra(0xFE303) -- EXTENSIBLE OF 0x0303
--
-- local function smashed(data,unicode,private)
--     local target = data.target
--     local height = target.parameters.xheight / 2
--     local c, done = accent_to_extensible(target,private,data.original,unicode,height,0,nil,-height,unicode)
--     if done then
--         c.topanchor = nil -- or maybe also all the others
--     end
--     return c
-- end
--
-- virtualcharacters[0xFE302] = function(data) return smashed(data,0x0302,0xFE302) end
-- virtualcharacters[0xFE303] = function(data) return smashed(data,0x0303,0xFE303) end

---------------------------------------------------------------------------------
-- these are moved to math-act.lmt
---------------------------------------------------------------------------------

-- local function reference(index,char)
--     if index then
--         return slotcommand[index][char]
--     else
--         return charcommand[char]
--     end
-- end
--
-- local function raised(data,replacement,down)
--     local character = data.scriptdata.characters[replacement]
--     if character then
--         local size = data.size
--         return {
--             width    = character.width,
--             height   = character.height,
--             depth    = character.depth,
--             commands = {
--                 down and downcommand[size/4] or upcommand[size/2],
--                 reference(data.scriptindex,replacement)
--             }
--         }
--     end
-- end
--
-- virtualcharacters[0x207A] = function(data) return raised(data,0x002B)      end
-- virtualcharacters[0x207B] = function(data) return raised(data,0x2212)      end
-- virtualcharacters[0x208A] = function(data) return raised(data,0x002B,true) end
-- virtualcharacters[0x208B] = function(data) return raised(data,0x2212,true) end

---------------------------------------------------------------------------------
-- these are moved to math-act.lmt
---------------------------------------------------------------------------------

-- local function repeated(data,char,n,fraction)
--     local character = data.characters[char]
--     if character then
--         local width = character.width
--         local delta = width - character.italic -- width * fraction
--         local c = charcommand[char]
--         local r = rightcommand[right]
--         local commands = { }
--         for i=1,n-1 do
--             width = width + delta
--             commands[#commands+1] = c
--             commands[#commands+1] = -delta
--         end
--         commands[#commands+1] = c
--         return {
--             width    = width,
--             height   = character.height,
--             depth    = character.depth,
--             commands = commands,
--         }
--     end
-- end
--
-- virtualcharacters[0x222C] = function(data)
--     return repeated(data,0x222B,2,1/8)
-- end
--
-- virtualcharacters[0x222D] = function(data)
--     return repeated(data,0x222B,3,1/8)
-- end

---------------------------------------------------------------------------------
-- these are moved to math-act.lmt
---------------------------------------------------------------------------------

-- -- spacing (no need for a cache of widths)
--
-- local c_zero   = byte('0')
-- local c_period = byte('.')
--
-- local function spacefraction(data,fraction)
--     local width = fraction * data.target.parameters.space
--     return {
--         width    = width,
--      -- commands = { rightcommand[width] }
--     }
-- end
--
-- local function charfraction(data,char)
--     local width = data.target.characters[char].width
--     return {
--         width    = width,
--      -- commands = { rightcommand[width] }
--     }
-- end
--
-- local function quadfraction(data,fraction)
--     local width = fraction * data.target.parameters.quad
--     return {
--         width  = width,
--      -- commands = { rightcommand[width] }
--     }
-- end
--
-- virtualcharacters[0x00A0] = function(data) return spacefraction(data,1)        end -- nbsp
-- virtualcharacters[0x2000] = function(data) return quadfraction (data,1/2)      end -- enquad
-- virtualcharacters[0x2001] = function(data) return quadfraction (data,1)        end -- emquad
-- virtualcharacters[0x2002] = function(data) return quadfraction (data,1/2)      end -- enspace
-- virtualcharacters[0x2003] = function(data) return quadfraction (data,1)        end -- emspace
-- virtualcharacters[0x2004] = function(data) return quadfraction (data,1/3)      end -- threeperemspace
-- virtualcharacters[0x2005] = function(data) return quadfraction (data,1/4)      end -- fourperemspace
-- virtualcharacters[0x2006] = function(data) return quadfraction (data,1/6)      end -- sixperemspace
-- virtualcharacters[0x2007] = function(data) return charfraction (data,c_zero)   end -- figurespace
-- virtualcharacters[0x2008] = function(data) return charfraction (data,c_period) end -- punctuationspace
-- virtualcharacters[0x2009] = function(data) return quadfraction (data,1/8)      end -- breakablethinspace
-- virtualcharacters[0x200A] = function(data) return quadfraction (data,1/8)      end -- hairspace
-- virtualcharacters[0x200B] = function(data) return quadfraction (data,0)        end -- zerowidthspace
-- virtualcharacters[0x202F] = function(data) return quadfraction (data,1/8)      end -- narrownobreakspace
-- virtualcharacters[0x205F] = function(data) return spacefraction(data,1/2)      end -- math thinspace

-- -- another crazy hack .. doesn't work as we define scrscr first .. we now have smaller
-- -- primes so we have smaller primes for the moment, big ones will become an option ..
-- -- these primes in fonts are a real mess .. kind of a dead end, so don't wonder about
-- -- the values below
--
-- local function smashed(data,unicode,optional)
--     local oldchar = data.characters[unicode]
--     if oldchar then
--         local height  = 0.85 * data.target.mathparameters.AccentBaseHeight
--         local newchar = table.copy(oldchar)
--         newchar.yoffset = height - oldchar.height
--         newchar.height  = height
--         return newchar
--     elseif not optional then
--         report_fallbacks("missing %U prime in font %a",unicode,data.target.properties.fullname)
--     end
-- end
--
-- addextra(0xFE932) -- SMASHED PRIME 0x02032
-- addextra(0xFE933) -- SMASHED PRIME 0x02033
-- addextra(0xFE934) -- SMASHED PRIME 0x02034
-- addextra(0xFE957) -- SMASHED PRIME 0x02057
--
-- addextra(0xFE935) -- SMASHED BACKWARD PRIME 0x02035
-- addextra(0xFE936) -- SMASHED BACKWARD PRIME 0x02036
-- addextra(0xFE937) -- SMASHED BACKWARD PRIME 0x02037
--
-- virtualcharacters[0xFE932] = function(data) return smashed(data,0x02032) end
-- virtualcharacters[0xFE933] = function(data) return smashed(data,0x02033) end
-- virtualcharacters[0xFE934] = function(data) return smashed(data,0x02034) end
-- virtualcharacters[0xFE957] = function(data) return smashed(data,0x02057) end
--
-- virtualcharacters[0xFE935] = function(data) return smashed(data,0x02035,true) end
-- virtualcharacters[0xFE936] = function(data) return smashed(data,0x02036,true) end
-- virtualcharacters[0xFE937] = function(data) return smashed(data,0x02037,true) end
--
-- local hack = nil
--
-- function mathematics.getridofprime(target,original)
--     local mathparameters = original.mathparameters
--     if mathparameters and next(mathparameters) then
--         local changed = original.changed
--         if changed then
--             hack = changed[0x02032]
--             changed[0x02032] = nil
--             changed[0x02033] = nil
--             changed[0x02034] = nil
--             changed[0x02057] = nil
--             changed[0x02035] = nil
--             changed[0x02036] = nil
--             changed[0x02037] = nil
--         end
--     end
-- end
--
-- function mathematics.setridofprime(target,original)
--     local mathparameters = original.mathparameters
--     if mathparameters and next(mathparameters) and original.changed then
--         target.characters[0xFE931] = target.characters[hack or 0x2032]
--         hack = nil
--     end
-- end
--
-- utilities.sequencers.appendaction("beforecopyingcharacters","system","mathematics.getridofprime")
-- utilities.sequencers.appendaction("aftercopyingcharacters", "system","mathematics.setridofprime")

-- local list = {
--     { 0x02032, true  },
--     { 0x02033, true  },
--     { 0x02034, true  },
--     { 0x02057, true  },
--     { 0x02035, false },
--     { 0x02036, false },
--     { 0x02037, false },
-- }
--
-- function mathematics.fixprimes(target,original)
--     local mathparameters = original.mathparameters
--     if mathparameters and next(mathparameters) then
--         for i=1,#list do
--             local entry = list[i]
--             local char  = original.characters[entry[1]]
--             if char then
--                 local height  = 0.85 * orginal.mathparameters.AccentBaseHeight
--                 char.yoffset = height - char.height
--                 char.height  = height
--                 return char
--             elseif entry[1] then
--                 report_fallbacks("missing %U prime in font %a",unicode,original.properties.fullname)
--             end
--         end
--     end
-- end
--
-- utilities.sequencers.appendaction("beforecopyingcharacters","system","mathematics.fixprimes")

---------------------------------------------------------------------------------
-- this one is not used
---------------------------------------------------------------------------------

-- addextra(0xFE941) -- EXTREMELY IDENTICAL TO
--
-- virtualcharacters[0xFE941] = function(data) -- this character is only needed for mathpairs
--     local characters = data.target.characters
--     local parameters = data.target.parameters
--     local basechar   = characters[0x003D]
--     local width      = basechar.width or 0
--     local height     = basechar.height or 0
--     local depth      = basechar.depth or 0
--     return {
--         unicode   = 0xFE941,
--         width     = width,
--         height    = height,         -- we cheat (no time now)
--         depth     = depth,          -- we cheat (no time now)
--         commands  = {
--             upcommand[height/2], -- sort of works
--             charcommand[0x003D],
--             leftcommand[width],
--             downcommand[height],     -- sort of works
--             charcommand[0x003D],
--         },
--     }
-- end

---------------------------------------------------------------------------------
-- these might move to math-act.lmt
---------------------------------------------------------------------------------
--
-- actuarian (beware: xits has an ugly one)

-- addextra(0xFE940) -- SMALL ANNUITY SYMBOL
--
-- local function actuarian(data)
--     local characters = data.target.characters
--     local parameters = data.target.parameters
--     local basechar   = characters[0x0078] -- x (0x0058 X) or 0x1D431
--     local linewidth  = parameters.xheight / 10
--     local basewidth  = basechar.width
--     local baseheight = basechar.height
--     return {
--         -- todo: add alttext
--         -- compromise: lm has large hooks e.g. \actuarial{a}
--         width    = basewidth + 4 * linewidth,
--         height   = basechar.height,
--         depth    = basechar.depth,
--         unicode  = 0x20E7,
--         commands = {
--             rightcommand[2 * linewidth],
--             downcommand[- baseheight - 3 * linewidth],
--             { "rule", linewidth, basewidth + 4 * linewidth },
--             leftcommand[linewidth],
--             downcommand[baseheight + 4 * linewidth],
--             { "rule", baseheight + 5 * linewidth, linewidth },
--         },
--     }
-- end
--
-- virtualcharacters[0x020E7] = actuarian -- checked
-- -----------------[0xFE940] = actuarian -- unchecked

-- local function equals(data,unicode,snippet,advance,n) -- mathpair needs them
--     local characters = data.target.characters
--     local parameters = data.target.parameters
--     local basechar   = characters[snippet]
--     local width      = n*basechar.width
--     local advance    = advance * parameters.quad -- for equals
--     return {
--         unicode  = unicode,
--         width    = width - (n-1)*advance,
--         height   = basechar.height,
--         depth    = basechar.depth,
--         commands = {
--             charcommand[snippet],
--             leftcommand[advance],
--             charcommand[snippet],
--             n > 2 and leftcommand[advance] or nil,
--             n > 2 and charcommand[snippet] or nil,
--         },
--     }
-- end
--
-- virtualcharacters[0x2A75] = function(data) return equals(data,0x2A75,0x003D, 1/5,2) end -- ==
-- virtualcharacters[0x2A76] = function(data) return equals(data,0x2A76,0x003D, 1/5,3) end -- ===
--
-- local function bars(data,unicode,snippet,advance,n) -- mathpair needs them
--     local characters = data.target.characters
--     local parameters = data.target.parameters
--     local basechar   = characters[snippet]
--     local width      = n*basechar.width
--     advance = advance * width
--     return {
--         unicode  = unicode,
--         width    = width - (n-1)*advance,
--         height   = basechar.height,
--         depth    = basechar.depth,
--         callback = "devirtualize",
--         commands = {
--             charcommand[snippet],
--             leftcommand[advance],
--             charcommand[snippet],
--             n > 2 and leftcommand[advance] or nil,
--             n > 2 and charcommand[snippet] or nil,
--         },
--     }
-- end
--
-- virtualcharacters[0x2980] = function(data) return bars(data,0x2980,0x007C,1/10,3) end -- |||

---------------------------------------------------------------------------------
-- these might move to math-act.lmt -- lucida needs this -- no longer used
---------------------------------------------------------------------------------

-- virtualcharacters[0x305] = function(data)
--     local target = data.target
--     local height = target.parameters.xheight/8
--     local width  = target.parameters.emwidth/2
--     local depth  = height
--     local used   = 0.8 * width
--     return {
--         width    = width,
--         height   = height,
--         depth    = depth,
--         commands = { { "rule", height, width } },
--         hparts   = {
--             {
--               advance   = width,
--               ["end"]   = used,
--               glyph     = 0x305,
--               start     = 0,
--             },
--             {
--               advance   = width,
--               ["end"]   = 0,
--               extender  = 1,
--               glyph     = 0x305,
--               start     = used,
--             },
--         }
--     }
-- end

-- local function threedots(data,shift)
--     local characters = data.target.characters
--     local parameters = data.target.parameters
--     local periodchar = characters[0x002E]
--     local pluschar   = characters[0x002B]
--     local period     = charcommand[0x002E]
--     local periodwd   = periodchar.width  or 0
--     local periodht   = periodchar.height or 0
--     local perioddp   = periodchar.depth or 0
--     local offset     = 0
--     if shift then
--         local plusht = pluschar.height or 0
--         local plusdp = pluschar.depth or 0
--         local axis   = (plusdp + plusht)//2 - plusdp
--         offset   = axis - periodht//2
--         periodht = axis + periodht//2
--     end
--     return {
--         width    = 3*periodwd,
--         height   = periodht,
--         depth    = 0,
--         commands = { upcommand[offset], period, period, period }
--     }
-- end
--
-- virtualcharacters[0x2026] = function(data) return threedots(data,false) end -- virtualforced[0x2026] = true
-- virtualcharacters[0x22EF] = function(data) return threedots(data, true) end -- virtualforced[0x22EF] = true