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

local sub, gsub = string.sub, string.gsub
local utfchar, utfvalues = utf.char, utf.values
local insert = table.insert
local setmetatableindex, concat = table.setmetatableindex, table.concat

local structurestags = structures.tags
local specifications = structurestags.specifications
local locatedtag     = structurestags.locatedtag

local backend        = structurestags.backend

local setattribute   = backend.setattribute
local extras         = backend.extras
local checks         = backend.checks
local finalizers     = backend.finalizers

----- bpfactor       = number.dimenfactors.bp
----- f_points       = string.formatters["%p"]
local f_em           = string.formatters["%.6Nem"]

local implement      = interfaces.implement

local mathmlns       <const> = "http://www.w3.org/1998/Math/MathML"

do

    ----- automathrows   = true  directives.register("export.math.autorows",   function(v) automathrows   = v end)
    ----- automathapply  = true  directives.register("export.math.autoapply",  function(v) automathapply  = v end)
    ----- automathnumber = true  directives.register("export.math.autonumber", function(v) automathnumber = v end)
    local automathstrip  = true  directives.register("export.math.autostrip",  function(v) automathstrip  = v end)

    local functions      = mathematics.categories.functions
    local tagging        = mathematics.tagging
    local functiontype   = mathematics.functiontype

    local function collapse(di,i,data,ndata,detail,element)
        local collapsing = di.data
        if data then
            di.element = element
            di.detail = nil
            i = i + 1
            while i <= ndata do
                local dn = data[i]
                if dn.detail == detail then
                    collapsing[#collapsing+1] = dn.data[1]
                    dn.skip = "ignore"
                    i = i + 1
                else
                    break
                end
            end
        end
        return i
    end

    local function collapse_all_mn(data)
        local n = #data
        local f = false
        local l = false
        local d = false
        local p = false
        for i=1,n do
            local di = data[i]
            local tg = di.tg
            if tg == "mn" then
                if not f then
                    d = di.data
                    f = i
                    p = false
                else
                    if p then
                        p.element = "mn"
                        local s = specifications[p.fulltag]
                        s.mathcharacter = nil
                        s.mathclass     = nil
                        s.mathgroup     = nil
                        s.mathindex     = nil
                    end
                    d[#d+1] = di.data[1]
                    data[i] = false
                    p = false
                end
                l = i
            elseif tg == "mi" or tg == "mc" then
                if p then
                    f = false
                end
                if i < n and data[i+1].tg == "mn" then
                    local d1 = di.data[1]
                    if d1 then
                        local c = d1.content
                        local s = specifications[di.fulltag]
                        if s.mathclass == "ordinary" and c and (c == "." or c == ",") then
                            if not f then
                                d = di.data
                                f = i
                                l = i
                                p = di
                            else
                                d[#d+1] = d1
                                data[i] = false
                            end
                        else
                            f = false
                        end
                    else
                        f = false
                    end
                else
                    f = false
                end
            elseif f and (tg == "msub" or tg == "msup" or tg == "msubsup") then
                local d1 = di.data[1]
                if d1 and d1.tg == "mn" then
                    d[#d+1] = d1.data[1]
                    d1.data = d
                    data[f] = false
                end
                f = false
            else
                f = false
            end
        end
        if d then
            local j = 0
            for i=1,n do
                local d = data[i]
                if d then
                    j = j + 1
                    data[j] = d
                end
            end
            for i=j+1,n do
                data[i] = nil
            end
        end
    end

    local functioncontent = { }

    setmetatableindex(functioncontent,function(t,k)
        local v = { { content = k } }
        t[k] = v
        return v
    end)

    local dummy_nucleus = {
        element   = "mtext",
        data      = { content = "" },
        nature    = "mixed",
        comment   = "dummy nucleus",
        fulltag   = "mtext>0"
    }

    local function accentchar(d) -- see mkiv for old one
        local detail = tonumber(d.detail)
        if detail then
            local d1 = d.data[1]
            if d1 and d1.tg == "mrow" then
                --
                d.element = "mrow" -- used
                d.detail = nil
                local s = specifications[d.fulltag] -- hm, used when not set
                s.detail = nil
                --
                d1.element = "mo" -- used
             -- d1.detail = nil
                d1.attributes = { stretchy = "true" }
                d1.nature = "mixed"
                d1.data = { { content = utfchar(detail) } }
                return d
            end
        end
    end

    local function maybetext(d)
        if #d.data == 1 and d.data[1].content then
            d.element = "mtext"
        else -- maybe also check if d.data[1].content
            d.element = "mrow"
        end
        return d
    end

    local no_mrow = {

        math          = true,

        mrow          = true,
        mfenced       = true,
        mfrac         = true,
        mroot         = true,
        msqrt         = true,
        mtable        = true,
        mi            = true,
        mo            = true,
        mn            = true,
        mspace        = true,
        mtext         = true,

     -- mmultiscripts = true,
     -- mstacker      = true,
     -- mextensible   = true,
     -- mdelimited    = true,
    }

    -- we could make a stupid xml and then just use lpath to clean it up

    -- local separator <const> = utfchar(0x2061)

    -- local function markapplicationof(di,data,i)
    --     if i > 1 then
    --         local d0 = data[i-1]
    --         local at = d0.attributes
    --         if at then
    --             at.mathapplication = true
    --         else
    --             d0.attributes = {
    --                 mathapplication = true,
    --             }
    --         end
    --     end
    --     -- di.tg = "ignore"
    --     -- di.skip = "ignore"
    -- end

    local function checked(d,n)
        if n == 1 then
            local di = d[1]
            if di then
                local tg = di.tg
                if tg == "ignore" then
                    -- todo: we can move ignore's data one level up
                    return 1
                elseif di.content then
                    return 1
                else
                    local dd = di.data
                    local nn = #dd
                    if nn > 0 and checked(dd,nn) > 0 then
                        return 1
                    else
                        return 0
                    end
                end
            else
                -- kind of weird
                return 0
            end
        else
            local m = 0
            for i=1,n do
                local di = d[i]
                if di then
                    local tg = di.tg
                    if tg == "ignore" then
                        -- skip
                    elseif di.content then
                        m = m + 1
                        d[m] = di
                    else
                        local dd = di.data
                        local nn = #dd
                        if nn > 0 and checked(dd,nn) > 0 then
                            m = m + 1
                            d[m] = di
                        end
                    end
                else
                    -- kind of weird
                end
            end
            if m < n then
                for i=n,m+1,-1 do
                    d[i] = nil
                end
            end
            return m
        end
    end

    local stretched = {
        operator = "false",
        open     = "false",
        close    = "false",
        middle   = "false",
        integral = "false",
    }

    local nbsp <const> = utfchar(0x00A0) -- &#0160;
    local mbsp <const> = utfchar(0x2000) -- after : ; ,

--     ," ",nbsp

    local replacer = lpeg.replacer {
        [", "] = ",".. mbsp,
        [". "] = ".".. mbsp,
        [": "] = ":".. mbsp,
        ["; "] = ";".. mbsp,
        [","]  = ",".. mbsp,
        ["."]  = ".".. mbsp,
        [":"]  = ":".. mbsp,
        [";"]  = ";".. mbsp,
        [" "]  =       nbsp,
    }


    local function checkmath(root) -- we can provide utf.toentities as an option
        local data = root.data
        if data then
            local ndata = #data
            local roottg = root.tg
            if roottg == "mo" then
                local s         = specifications[root.fulltag]
                local class     = s.mathclass
                local group     = s.mathgroup
                local delimiter = s.delimiter
-- why not print(s.accent)
                if class or group then
                    root.attributes = {
                        mathclass     = class,
                        mathgroup     = group,
                        mathindex     = s.mathindex,
                        mathcharacter = s.mathcharacter,
                        mathstack     = s.mathstack,
                        stretchy      = (delimiter == "true" and "true") or stretched[class] or nil,
                    }
                else
                    -- todo: stackers, accents etc
-- we can put an accent class on the char
                    root.attributes = {
                        mathstack = s.mathstack,
                     -- stretchy  = "false",
                        stretchy  = delimiter == "true" and "true" or "false", -- too much now
                    }
                end
            elseif roottg == "mfenced" then
                local s = specifications[root.fulltag]
                local o = s.operator
                if o then
                    root.skip = "comment"
                 -- root.content = utfchar(o) -- use embedded for now
                elseif tagging.mfenced then
                    local l = s.left
                    local m = s.middle
                    local r = s.right
                    if l then
                        l = utfchar(l)
                    end
                    if m then
                        local t = { }
                        for i=1,#m do
                            t[i] = utfchar(m[i])
                        end
                        m = concat(t)
                    end
                    if r then
                        r = utfchar(r)
                    end
                    root.attributes = {
                        open       = l,
                        separators = m,
                        close      = r,
                        stretchy   = "true",
                    }
                else
                    root.element    = "mrow"
                    root.attributes = {
                        mathcategory = s.mathcategory,
                     -- stretchy     = "true", -- not needed, more a signal
                    }
                end
         -- elseif roottg == "mstacker" then
            elseif roottg == "mrow" then
                ndata = checked(data,ndata)
            end
            if ndata == 0 then
                root.skip = "comment" -- get rid of weird artefacts
                root.nota = "weird"
                return
            elseif ndata == 1 then
                local d = data[1]
                if not d or d == "" then
                    root.skip = "comment"
                    return
                elseif d.content then
                    return
                elseif roottg == "mrow" or roottg == "mtext" then
                    -- maybe just always ! check spec first
                    -- or we can have checks.* for each as we then can flatten
                    local s = specifications[root.fulltag]
                    if s.mathunit then
                        d.attributes = {
                            mathunit = s.mathunit
                        }
                    elseif s.mathdigits then
                        d.attributes = {
                            mathdigits = s.mathdigits
                        }
                    elseif s.mathfunction then
                        d.attributes = {
                           mathfunction = s.mathfunction,
                           mathcategory = s.mathcategory,
                           mathstack    = s.mathstack,
                        }
                    elseif no_mrow[d.tg] then
                        root.skip = "comment"
                    else
                        d.attributes = {
                           mathstack = s.mathstack,
                        }
                    end
                elseif roottg == "mo" then
                    if d.tg == "mo" then
                        root.skip = "comment"
                    end
                end
            end
            -- todo
            local i = 1
            while i <= ndata do                   -- -- -- TOO MUCH NESTED CHECKING -- -- --
                local di = data[i]
                if di and not di.content then
                    local tg = di.tg
                    if tg == "math" then
                     -- di.element = "mrow" -- when properties
                        di.skip = "comment"
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mover" then
                        local s = specifications[di.fulltag]
                        if s.accent then
                            local t = s.top
                            local d = di.data
                            -- todo: accent = "false" (for scripts like limits)
                            di.attributes = {
                                accent       = "true",
                                mathcategory = s.mathcategory,
                            }
                            -- todo: p.topfixed
                            if t then
                                -- mover
                                if true then
                                    local dd = d[1].data
                                    if dd then
                                        dd[1].content = utfchar(t)
                                    end
                                end
                                --
                                di.data = { d[2], d[1] }
                            end
                        else
                            -- can't happen
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "munder" then
                        local s = specifications[di.fulltag]
                        if s.accent then
                            local b = s.bottom
                            local d = di.data
                            -- todo: accent = "false" (for scripts like limits)
                            di.attributes = {
                                accent       = "true",
                                mathcategory = s.mathcategory,
                            }
                         -- todo: p.bottomfixed
                            if b then
                                -- munder
                                if true then
                                    local dd = d[2].data
                                    if dd then
                                        dd[1].content = utfchar(b)
                                    end
                                end
                            end
                        else
                            -- can't happen
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "munderover" then
                        local s = specifications[di.fulltag]
                        if s.accent then
                            local t = s.top
                            local b = s.bottom
                            local d = di.data
                            -- todo: accent      = "false" (for scripts like limits)
                            -- todo: accentunder = "false" (for scripts like limits)
                            di.attributes = {
                                accent      = "true",
                                accentunder = "true",
                            }
                         -- todo: p.topfixed
                         -- todo: p.bottomfixed
                            if t and b then
                                -- munderover
                                if true then -- we don't go here any more
                                    local dd = d[1].data
                                    if dd then
                                        dd[1].content = utfchar(t)
                                    end
                                    local dd = d[3].data
                                    if dd then
                                        dd[1].content = utfchar(b)
                                    end
                                end
                                di.data = { d[2], d[3], d[1] }
                            else
                                -- can't happen
                            end
                        else
                            -- can't happen
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mstacker" then
                        local d = di.data
                        local d1 = d[1]
                        local d2 = d[2]
                        local d3 = d[3]
                        local t1 = d1 and d1.tg
                        local t2 = d2 and d2.tg
                        local t3 = d3 and d3.tg
                        local m  = nil -- d1.data[1]
                        local t  = nil
                        local b  = nil
                        -- only accent when top / bot have stretch
                        -- normally we flush [base under over] which is better for tagged pdf
                        if t1 == "mstackermid" then
                            if t2 == "mstackertop" then
                                if t3 == "mstackerbot" then
                                    m = accentchar(d1) or maybetext(d1)-- or m
                                    t = accentchar(d2) or maybetext(d2)
                                    b = accentchar(d3) or maybetext(d3)
                                    di.element = "munderover"
                                    di.data    = { m or d1.data[1], b, t }
                                else
                                    m = accentchar(d1) or maybetext(d1)-- or m
                                    t = accentchar(d2) or maybetext(d2)
                                    di.element = "mover"
                                    di.data    = { m or d1.data[1], t }
                                end
                            elseif t2 == "mstackerbot" then
                                if t3 == "mstackertop" then
                                    m = accentchar(d1) or maybetext(d1)-- or m
                                    b = accentchar(d2) or maybetext(d2)
                                    t = accentchar(d3) or maybetext(d3)
                                    di.element = "munderover"
                                    di.data    = { m or d1.data[1], t, b  }
                                else
                                    m = accentchar(d1) or maybetext(d1)-- or m
                                    b = accentchar(d2) or maybetext(d2)
                                    di.element = "munder"
                                    di.data    = { m or d1.data[1], b }
                                end
                            else
                                m = accentchar(d1) -- or m
                                di.element = "mrow"
                                di.data    = { m or d1.data[1] }
                            end
                        end
                        if t or b then
                            di.attributes = {
                                accent      = t and "true" or nil,
                                accentunder = b and "true" or nil,
                            }
                            di.detail = nil
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mroot" then
                        local data = di.data
                        local size = #data
                        if size == 1 then
                            -- else firefox complains ... code in math-tag (for pdf tagging)
                            di.element = "msqrt"
                        elseif size == 2 then
                            data[1], data[2] = data[2], data[1]
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mdelimited" then
                        local d = di.data
                        local n = #d
                        for i=1,n do
                            local di = d[i]
                            local properties = specifications[di.fulltag] or { }
                            local location = properties.delimiterlocation
                            if location then
                                if di.attributes then
                                    di.attributes.delimiterlocation = location
                                else
                                    -- useless and bad anyway
                                    di.attributes = { delimiterlocation = location }
                                end
                            end
                        end
                        di.element = "mrow"
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mstack" then
                        di.element = "mover"
                        local scriptlevel  = "1" -- "+1"
                        if di.attributes then
                            di.attributes.scriptlevel = scriptlevel
                        else
                            di.attributes = { scriptlevel = scriptlevel }
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "break" then
                        di.skip = "comment"
                        i = i + 1
                    elseif tg == "mspace" then
                     -- di.empty = true
                        local s = specifications[di.fulltag]
                        local e = s and s.emfactor
                        if e and e ~= 0 then
                            di.element = "mspace"
                            di.attributes = {
                                width = f_em(e),
                            }
                        end
                        i = i + 1
                    elseif tg == "mtext" then
                        -- this is only needed for unboxed mtexts ... all kind of special
                        -- tex border cases and optimizations ... trial and error
                        local data = di.data
                        local size = #data
-- bmatrix ...
                        if size > 1 then
                            for i=1,size do
                                local di = data[i]
                                local content = di.content
                                if content then
                                    data[i] = {
                                        element = "mtext",
                                        nature  = "inline",
                                        data    = { di },
                                        n       = 0,
                                    }
--                                     di.content = gsub(content," ",nbsp)
di.content = lpeg.match(replacer,content)
                                elseif di.tg == "math" then
                                    local di = di.data[1]
                                    if di then
                                        data[i] = di
                                        checkmath(di)
                                    end
                                end
                            end
                            di.element = "mrow"
                         -- di.tg = "mrow"
                         -- di.nature  = "inline"
                        elseif size > 0 then
                            local di = data[1]
                            local content = di.content
                            if content then
--                                 di.content = gsub(content," ",nbsp)
di.content = lpeg.match(replacer,content)
                            end
                        end
                        checkmath(di)
                        i = i + 1
                    elseif tg == "mi" then
                        local s = specifications[di.fulltag]
                        if s.mathclass == "punctuation" then
                            di.element = "mtext"
                            checkmath(di)
                            i = i + 1
                        else
                         -- if di.data[1].content == separator then
                         --     markapplicationof(di,data,i)
                         -- end
                            local class    = s.mathclass
                            local group    = s.mathgroup
                         -- local category = s.mathcategory
                            if class or group then
                                di.attributes = {
                                    mathclass     = class,
                                    mathgroup     = group,
                                    mathindex     = s.mathindex,
                                    mathcharacter = s.mathcharacter,
                                    mathstack     = s.mathstack,
                                }
                            else
                                di.attributes = {
                                    mathstack     = s.mathstack,
                                }
                            end
                            checkmath(di)
                            i = i + 1
                        end
                    elseif tg == "mrow" then
                        local d = di.data
                        local n = #d
                        local s = specifications[di.fulltag]
                        if s.mathunit then
                            di.attributes = { mathunit = s.mathunit }
                            i = i + 1
                        elseif s.mathdigits then
                            -- does this ever happen (if so check)
                            for i=1,n do
                                d[i] = d[i].data[1].content or ""
                            end
                            di.tg      = "mn"
                            di.element = "mn"
                            di.nature  = "mixed"
                            di.data    = { { content = concat(d) } }
                            i = i + 1
                        elseif s.mathfunction then
                            di.attributes = {
                                mathfunction = s.mathfunction,
                                mathstack    = s.mathstack
                            }
                            local category = tonumber(s.mathcategory)
                            if functiontype(category) == "function" then
                                local fnc = functions[category] -- functions[s.mathfunction]
                                local tag = fnc and fnc.tag
                                if tag then
                                    di.tg      = "mi"
                                    di.element = "mi"
                                    di.nature  = "mixed"
                                    di.data    = functioncontent[tag]
                                end
                            end
                            i = i + 1
                        elseif s.mathfunctionstack then
                            di.attributes = {
                                mathfunction      = s.mathfunction,
                                mathstack         = s.mathstack,
                                mathfunctionstack = s.mathfunctionstack,
                            }
                            checkmath(di)
                            i = i + 1
                        elseif s.mathdelimitedstack then
                            di.attributes = {
                                mathdelimitedstack = s.mathdelimitedstack,
                            }
                            checkmath(di)
                            i = i + 1
                        elseif s.mathfractionstack then
                            di.attributes = {
                                mathfractionstack = s.mathfractionstack,
                            }
                            checkmath(di)
                            i = i + 1
                        else
                            if n > 0 then
                                local d1 = d[1]
                                local tg = d1.tg
                                if tg == "mfrac" then
                                    if n == 1 then -- simple one
                                        di = d1
                                        data[i] = di
                                    elseif n == 2 and d[2].tg == "ignore" then -- simple one with nilled middle fence
                                        -- already wiped anyway
                                        di = d1
                                        data[i] = di
                                    end
--                                 elseif tg == "mo" then
-- if i > 1 and d1.data[1].content == separator then
--     markapplicationof(di,data,i)
-- end
                                end
                            end
                            checkmath(di)
                            i = i + 1
                        end
                    elseif tg == "formulacaption" then -- formulanumber
                        di.tg = "ignore"
                        i = i + 1
                    elseif tg == "subformula" then
                        di.tg = "mrow"
                        checkmath(di)
                        i = i + 1
                    else
                        -- or first check for tg
                        local s = specifications[di.fulltag]
                        if not s then
                            -- whatever
                        elseif tg == "mfrac" then
                            if s.mathfractionrule == "no" then
                                di.attributes = {
                                    rulethickness = "0"
                                }
                            end
                        elseif tg == "msup" then
                            if s.limits then
                                di.element = "mover"
                            end
                        elseif tg == "msub" then
                            if s.limits then
                                di.element = "munder"
                            end
                        elseif tg == "msubsup" then
                            if s.limits then
                                di.element = "munderover"
                            end
                        end
                        --
                        checkmath(di)
                        i = i + 1
                    end
                else -- can be string or boolean
                    if parenttg ~= "mtext" and di == " " then
                        data[i] = false
                    end
                    i = i + 1
                end
            end
        end
    end

    local function stripmath(di)
        if not di then
            --
        elseif di.content then
            return di
        else
            local tg = di.tg
            if tg == "mtext" or tg == "ms" then
                return di
            elseif tg == "mspace" then
                return di
            else
                local data = di.data
                local ndata = #data
                local n = 0
                for i=1,ndata do
                    local d = data[i]
                    if d and not d.content then
                        d = stripmath(d)
                    end
                    if d then
                        local content = d.content
--                         if d.tg == "mspace" then
--                             n = n + 1
--                             data[n] = d
--                             d.data = { }
--                         elseif not content then
--                             n = n + 1
--                             data[n] = d
--                             d.__i__ = n -- hm
--                         else
--                             n = n + 1
--                             data[n] = d
--                         end
                        n = n + 1
                        data[n] = d
                        if d.tg == "mspace" then
                            d.data = { }
                        elseif not content then
                            d.__i__ = n -- hm
                        end
                    end
                end
                for i=ndata,n+1,-1 do
                    data[i] = nil
                end
                -- maybe integrate the above and this one:
                collapse_all_mn(data)
                --
                if #data > 0 then
                    return di
                end
            end
        end
    end

    function checks.math(di)
-- inspect(di)
        if di.skip == "comment" then
            -- already done, kind of weird, happens in mathmatrix, maybe some collapse
            -- issue that i need to look into
        else
            local specification = specifications[di.fulltag]
            local mode   = specification.mode == "display" and "block" or "inline"
            local domain = specification.domain or "default"
            local family = specification.family or "regular"
            local style  = specification.style or 2 -- text
            di.attributes = {
             -- ["xmlns:m"]          = mathmlns,
                ["xmlns"]            = mathmlns,
                ["display"]          = mode,
                ["alttext"]          = specification.input, -- bonus, will go
             -- ["class"]            = style < 2 and ".math_display_style" or ".math_text_style",
                ["displaystyle"]     = style < 2 and "true" or "false",
                ["data-lmtx-blob"]   = specification.blob,
                ["data-lmtx-domain"] = domain ~= "default" and domain or nil,
                ["data-lmtx-family"] = family ~= "regular" and family or nil,
            }
            -- can be option if needed:
            if specification.standalone then
                di.nature = "display"
            elseif mode == "inline" then
             -- di.nature = "mixed"  -- else spacing problem (maybe inline)
                di.nature = "inline" -- we need to catch x$X$x and x $X$ x
            else
                di.nature = "display"
            end
            if automathstrip then
                stripmath(di)
            end
            checkmath(di)
        end
    end

    -- this one can replace some of the previous code .. todo (test on mathmatrix)

    local mprescripts = {
        element = "mprescripts",
        data    = { content = "" },
        nature  = "inline", -- mixed
        fulltag = "mprescripts>0"
    }

    local function wrapup(d,index,n,prelist,kernel,postlist)
        local di   = d[index]
        local post = #postlist
        local pre  = #prelist
        local list = { kernel }
        local size = 1
        for i=index+1,n do
            d[i].skip = "ignore"
        end
        if post > 0 then
            for i=1,post do
                size = size + 1 ; list[size] = postlist[i]
            end
        end
        if pre > 0 then
            size = size + 1 ; list[size] = mprescripts
            for i=1,pre do
                size = size + 1 ; list[size] = prelist[i]
            end
        end
        di.element        = "mmultiscripts"
     -- di.tg             = "mmultiscripts"
        di.data           = list
        di.iscontinuation = true
        di.__i__          = size
    end

    local function found(d,what)
        if what then
            for i=1,#d do
                local di = d[i]
                local sp = specifications[di.fulltag]
                if sp and sp.script == what then
                    return di
                end
            end
        else
            for i=1,#d do
                local di = d[i]
                local sp = specifications[di.fulltag]
                if not sp or not sp.script then
                    return di
                end
            end
        end
    end

    -- todo: pick up kernel

    function checks.mrow(di)
        local d = di.data
        if d then
            local postlist = nil
            local prelist  = nil
            local kernel   = nil
            local index    = 0
            for i=1,#d do
                local di   = d[i]
                local data = di.data
                local tg   = di and di.tg
                local sp   = specifications[di.fulltag]
                local continuation = sp and sp.continuation
                if continuation then
                    -- head kernel next
                    if postlist and continuation.head then
                        wrapup(d,index,#d,prelist,kernel,postlist)
                        postlist = nil
                        prelist  = nil
                        kernel   = 0
                    end
                    -- play safe as we can have empty ones (so maybe move the extra code here)
                    local nd = #data
                    if tg == "msup" then
                        if not postlist then
                            index    = i
                            postlist = { }
                            prelist  = { }
                            kernel   = dummy_nucleus
                        end
                        local sup = found(data,"sup")
                        postlist[#postlist+1] = dummy_nucleus
                        postlist[#postlist+1] = sup
                        if continuation.kernel then
                            kernel = data[1] or dummy_nucleus
                        end
                    elseif tg == "msub" then
                        if not postlist then
                            index    = i
                            postlist = { }
                            prelist  = { }
                            kernel   = dummy_nucleus
                        end
                        local sub = found(data,"sub")
                        postlist[#postlist+1] = sub
                        postlist[#postlist+1] = dummy_nucleus
                        if continuation.kernel then
                            kernel = data[1] or dummy_nucleus
                        end
                    elseif tg == "msubsup" then
                        if not postlist then
                            index    = i
                            postlist = { }
                            prelist  = { }
                            kernel   = dummy_nucleus
                        end
                        local sub = found(data,"sub")
                        local sup = found(data,"sup")
                        postlist[#postlist+1] = sub or dummy_nucleus
                        postlist[#postlist+1] = sup or dummy_nucleus
                        if continuation.kernel then
                            kernel = data[1] or dummy_nucleus
                        end
                    elseif tg == "mmultiscripts" then
                        -- we know that we only have one set
                        if not postlist then
                            index    = i
                            postlist = { }
                            prelist  = { }
                            kernel   = dummy_nucleus
                        end
                        local prime  = found(data,"prime")
                        local sub    = found(data,"sub")
                        local sup    = found(data,"sup")
                        local presub = found(data,"presub")
                        local presup = found(data,"presup")
                        if prime then
                            postlist[#postlist+1] = dummy_nucleus
                            postlist[#postlist+1] = prime
                        end
                        if sub or sup then
                            postlist[#postlist+1] = sub or dummy_nucleus
                            postlist[#postlist+1] = sup or dummy_nucleus
                        end
                        if presub or presup then
                            prelist[#prelist+1] = presub or dummy_nucleus
                            prelist[#prelist+1] = presup or dummy_nucleus
                        end
                        if continuation.kernel then
                            kernel = data[1] or dummy_nucleus
                        end
                    else
                        postlist = nil
                        prelist  = nil
                        kernel   = nil
                    end
                elseif postlist then
                    wrapup(d,index,i-1,prelist,kernel,postlist)
                    postlist = nil
                    prelist  = nil
                    kernel   = nil
                end
            end
            if postlist then
                wrapup(d,index,#d,prelist,kernel,postlist)
            end
        end
    end

    -- we can move more checks here

    local function flatten(di)
        local r = di.__p__
        while r do
            local d = r.data
            local n = #d
            if d and n > 1 then
                n = checked(d,n)
            end
            local tg = r.tg
            if n == 1 and (tg == "mtext" or tg == "mrow") then
                r.skip = "comment" -- weird error
                r = r.__p__
            else
                break
            end
        end
    end

    function checks.mtable(di)
        flatten(di)
        local d = di.data
-- -- left / right
-- -- local main   = { }
-- -- local left   = { }
-- local max    = 0
-- --
-- for i=1,#d do
--     local d = d[i]
--     if d.tg == "mtr" then
--         if #d.data > max then
--             max = #d.data
--         end
--     end
-- end
-- for i=1,#d do
--     local d = d[i]
--     if d.tg == "mtr" then
--         if #d.data < max then
--             local first = d.data[1]
--             specifications[first.fulltag].cols = max
--             first.attributes = { columnspan = max }
--         end
--     end
-- end

-- if next(left) then
--     max = max + 1
--     for i=1,#main do
--         insert(main[i].data,1,left[i] or {
--             tg      = "mtd",
--             element = "mtd",
--             nature  = "mixed",
--             data    = { },
--         })
--     end
-- end
--     for i=1,#main do
-- print(#main[i].data,max)
--         if #main[i].data < max then
--             insert(main[i].data,{
--                 tg      = "mtd",
--                 element = "mtd",
--                 nature  = "mixed",
--                 data    = { },
--             })
--         end
--     end
-- -- if next(right) then
-- --     for i=1,#main do
-- --         insert(main[i].data,right[i] or {
-- --             tg      = "mtd",
-- --             element = "mtd",
-- --             nature  = "mixed",
-- --             data    = { },
-- --         })
-- --     end
-- -- end
-- di.data = main
         for i=1,#d do
             local d = d[i]
             if d.tg == "mtr" then
                 local d = d.data
                 for i=1,#d do
                     local d = d[i]
                     if d.tg == "mtd" then
                         -- okay
                     elseif d.content then
                         d.content = ""
                     else
                         d.skip = "comment" -- weird error
                     end
                 end
             elseif d.content then
                 d.content = ""
             else
                 d.skip = "comment" -- weird error
             end
         end
    end

    function extras.mmultiscripts(di,element,n,fulltag)
        if not di.iscontinuation then
            local d      = di.data
            local sup    = found(d,"sup")
            local sub    = found(d,"sub")
            local presup = found(d,"presup")
            local presub = found(d,"presub")
            local prime  = found(d,"prime")
            local n = 1
            if sup or sub then
                n = n + 1 ; d[n] = sub or dummy_nucleus
                n = n + 1 ; d[n] = sup or dummy_nucleus
            end
            if prime then
                n = n + 1 ; d[n] = dummy_nucleus
                n = n + 1 ; d[n] = prime
            end
            if presup or presub then
                n = n + 1 ; d[n] = mprescripts
                n = n + 1 ; d[n] = presub or dummy_nucleus
                n = n + 1 ; d[n] = presup or dummy_nucleus
            end
            d.__i__ = n
        end
    end

    function extras.msub(di,element,n,fulltag)
        local data = di.data
        local nuc = found(data)
        local sub = found(data,"sub")
        data[1] = nuc or dummy_nucleus
        data[2] = sub or dummy_nucleus
        data.__i__ = 2
        local sp = specifications[di.fulltag]
        if attributes then
            attributes.mathsubindex = sp.subindexed
        else
            di.attributes = {
                mathsubindex = sp.subindexed,
            }
        end
    end

    function extras.msup(di,element,n,fulltag)
        local data = di.data
        local nuc = found(data)
        local sup = found(data,"sup")
or found(data,"prime")
        data[1] = nuc or dummy_nucleus
        data[2] = sup or dummy_nucleus
        data.__i__ = 2
        local sp = specifications[di.fulltag]
        local attributes = di.attributes
        if attributes then
            attributes.mathsupindex = sp.supindexed
        else
            di.attributes = {
                mathsupindex = sp.supindexed,
            }
        end
    end

    function extras.msubsup(di,element,n,fulltag)
        local data = di.data
        local nuc = found(data)
        local sup = found(data,"sup")
or found(data,"prime")
        local sub = found(data,"sub")
        data[1] = nuc or dummy_nucleus
        data[2] = sub or dummy_nucleus
        data[3] = sup or dummy_nucleus
        data.__i__ = 3
        local sp = specifications[di.fulltag]
        if attributes then
            attributes.mathsupindex = sp.supindexed
            attributes.mathsubindex = sp.subindexed
        else
            di.attributes = {
                mathsupindex = sp.supindexed,
                mathsubindex = sp.subindexed,
            }
        end
    end

    function extras.munder(di,element,n,fulltag)
        if di.tg == "msub" then
            extras.msub(di,element,n,fulltag)
        end
    end

    function extras.mover(di,element,n,fulltag)
        if di.tg == "msup" then
            extras.msup(di,element,n,fulltag)
        end
    end

    function extras.munderover(di,element,n,fulltag)
        if di.tg == "msubsup" then
            extras.msubsup(di,element,n,fulltag)
        end
    end

end