Re: [tex4ht] domfilter errors with the new option fastmathjax when using breqn.

[Michal Hoftich]

Hi Nasser,

Finally I am now able to make MWE that shows this issue and see
> its effect in the HTML.
>
> I use breqn heavily in the code and Michal made a nice
> filter for make4ht which automatically changes all dmath* to
> align* when translating to mathjax. It is called config.lua
> which I put in $HOME/.config/make4ht/config.lua
>


In this case, you can try this version of the build file. It escapes < and
> in Dmath. If you have problems with other math environments, it would
need  an update.

Best regards,
Michal

local filter = require "make4ht-filter"
local domfilter = require "make4ht-domfilter"

local function process_options(options)
  -- convert [number={foo}] to \tag{foo}
  local number = options:match("number%s*=%s*{?(%w+)")
  if number then
    return "\\tag{" .. number .. "}"
  end
  return ""
end


local function escape_equal(str)
  -- there can be multiple equal characters in the string. we should put the & character
  -- just before the one which is not inside any group
  -- escape nested equal signs
  str = str:gsub("({[^{^}]+)=([^{^}]+})", "%1:EQUAL:%2")
  -- replace remaining =
  str = str:gsub("([^\n]+)", function(line)
    line = line:gsub("=", "&=", 1)
    return line .. "\n"
  end)
  -- str = str:gsub("=", "&=")
  -- return escaped =
  str = str:gsub(":EQUAL:", "=")
  return str
end

local function make_align(dgroup, new_env)
  -- change breqn environment contents to align*
  -- change = to &=
  -- local dgroup = escape_equal(dgroup) -- <- we don't do this anymore, it leads only to problems
  local new_env = new_env or  "\\begin{align*}\n%s\n\\end{align*}"
  dgroup = dgroup:gsub(">", "&gt;"):gsub("<", "&lt;")
  -- return the fixed text in align* environment
  -- return "\\begin{".. new_env .."}" ..  dgroup .. "\\end{" .. new_env .. "}"
  return string.format(new_env, dgroup)
end

-- process remaining dmath environments
local function process_dmath(s, env_name, new_env)
  return s:gsub("\\begin%s*{" .. env_name .. "}(.-)\\end%s*{" .. env_name .. "}",
  function(dmath)
    -- options can be still here
    local dmath = dmath:gsub("^%s*(%b[])", process_options)
    return make_align(dmath, new_env)
  end)
end

local function process_dgroup(s, env_name)
  return s:gsub("\\begin%s*{" .. env_name .. "}(.-)\\end%s*{" .. env_name .. "}",
  function(dgroup)
    -- remove environemnts
    dgroup = process_dmath(dgroup, "dmath%*", "\n%s\\\\\n")
    dgroup = process_dmath(dgroup, "dmath", "\n%s\\\\\n")
    local dgroup = escape_equal(dgroup) -- <- we don't do this anymore, it leads only to problems
    return make_align(dgroup)
  end)
end


local process = filter {
  -- find all dgroup* environments and convert them to align*
  function(s)
    local s = process_dgroup(s,"dgroup%*")
    s = process_dgroup(s, "dgroup")
    -- process remaining dmath environments in the document
    s = process_dmath(s, "dmath%*", "\\[\n%s\n\\]")
    s = process_dmath(s, "dmath", "\\begin{equation}\n%s\n \\end{equation}")
    return s
  end,

}
-- install filter to match HTML files
Make:match("html?$", process)