On 12/11/2018 11:34 AM, mf wrote:

But i should consider all the text parts with a modified kerning and disable kerning around character sequences like "ff", "ffi", "fl" and so on. Luckily, the XHTML markup "knows" where the kerning is modified:

<p class="wide">A paragraph with a modified kerning</p>

should become

<p class="wide">A paragraph with a modi<dk>fi</dk>ed kerning</p>

Where <dk>...</dk> (dk=Disable Kerning) are tags to be inserted automatically before feeding the XHTML into ConTeXt.
I'm not very happy or proud about it, but it can be done.
Do you think it can be better done inside ConTeXt?

I nearly managed to do it in ConTeXt, but I can't create the "<dk>" elements right (the "new_dk_element" function is wrong):

did you play with

\definefontfeature[whatever][keepligatures=auto]

\definecharacterkerning [extrakerning] [factor=0.125,features=whatever]

\starttext
    \setcharacterkerning[extrakerning]
    effe fietsen
\stoptext




\startbuffer[test]
<text>
<p>Some ligatures: float, finance, affine, affluent.</p>
<p>Modified kerning:</p>
<p class="narrow">Some ligatures: float, finance, affine, affluent.</p>
<p class="wide">Some ligatures: float, finance, affine, affluent.</p>
</text>
\stopbuffer

\startluacode
local function new_dk_element( parent, text )
   return {
     tag     = "dk",
     ns      = "",
     rn      = "",
     dt      = { text },
     at      = {},
     command = "xml:dk",
     __p__   = parent
   }
--[[
   local t = xml.toxml( "<dk>" .. text .. "</dk>" )
   t.__p__ = parent
   return t
]]--
end

local append = table.insert
local function saveLigaturesFromKerning( t )
   if t and t.dt then
     local dt = t.dt
     local t_copy = {}
     for k,v in pairs( t ) do
       if k ~= "dt" then t_copy[ k ] = v end
     end
     local new_dt = {}
     local i
     local child
     local b, e
     for i = 1, #dt, 1 do
       child = dt[ i ]
       if type( child ) == "string" then
         local s = child
         repeat
           b, e = string.find( s, "f?f[il]" )
           if b then
             if b > 1 then append( new_dt, string.sub( s, 1, b - 1 ) ) end
             append( new_dt, new_dk_element( t, string.sub( s, b, e ) ) )
--            append( new_dt, "[" .. string.sub( s, b, e ) .. "]" )
             s = string.sub( s, e + 1 )
           else
             append( new_dt, s )
           end
         until not b
       else
         append( new_dt, child )
       end
     end
     t.dt = new_dt
   end
   return t
end

function xml.functions.textWithKerning( t )
   local kt = saveLigaturesFromKerning( t )
   lxml.flush( kt )
end
\stopluacode

\definecharacterkerning[narrow][factor=-.02]
\definecharacterkerning[wide][factor=.02]
\def\Narrow#1{\bgroup\setcharacterkerning[narrow]#1\egroup}
\def\Wide#1{\bgroup\setcharacterkerning[wide]#1\egroup}
\def\NoKerning#1{\bgroup\resetcharacterkerning #1\egroup}

\startxmlsetups xml:test
   \xmlsetsetup{#1}{text|p|dk}{xml:*}
   \xmlsetsetup{#1}{{p.narrow}}{xml:p:narrow}
   \xmlsetsetup{#1}{{p.wide}}{xml:p:wide}
\stopxmlsetups

\xmlregistersetup{xml:test}

\startxmlsetups xml:text
   \xmlflush{#1}
\stopxmlsetups

\startxmlsetups xml:p
   \xmlflush{#1}\par
\stopxmlsetups

\startxmlsetups xml:p:narrow
   \Narrow{\xmlfunction{#1}{textWithKerning}}\par
\stopxmlsetups

\startxmlsetups xml:p:wide
   \Wide{\xmlfunction{#1}{textWithKerning}}\par
\stopxmlsetups

\startxmlsetups xml:dk
   \NoKerning{\red\xmlflush{#1}}
\stopxmlsetups

\starttext
   \xmlprocessbuffer{xml:test}{test}{}
\stoptext

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