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

if not context then return end

local equaldigits = { }

-- for i=48,57 do
--     equaldigits[i] = fonts.helpers.newprivateslot(tonumber(i)..".equaldigits")
-- end

local function initialize(tfmdata,value)
    if value then
        local characters = tfmdata.characters
        local wd, ht, dp = 0, 0, 0
        for i=48,57 do
            if not equaldigits[i] then
                equaldigits[i] = fonts.helpers.newprivateslot(tonumber(i)..".equaldigits")
            end
            local c = characters[i]
            local w = c.width  or 0
            local h = c.height or 0
            local d = c.depth  or 0
            if w > wd then wd = w end
            if h > ht then ht = h end
            if d > dp then dp = d end
        end
        for i=48,57 do
         -- fonts.helpers.addprivate(tfmdata,tonumber(i)..".equaldigits")
            local u = equaldigits[i]
            local c = characters[i]
            characters[u] = table.setmetatableindex( {
               height  = ht,
               depth   = dp,
               width   = wd,
               xoffset = (wd - (c.width  or 0)) / 2,
           }, c)
        end
    end
end

fonts.handlers.otf.features.register {
    name        = "equaldigits",
    description = "equaldigits",
    manipulators = {
        base = initialize,
        node = initialize,
    }
}

fonts.handlers.otf.addfeature {
 -- name    = "tnum", -- let's not waste that one
    name    = "tabledigits",
    type    = "substitution",
    nocheck = true,
    data    = equaldigits,
}