%D \module
%D   [       file=lang-ovl,
%D        version=2016.02.03, % about that time (maybe earlier)
%D          title=\CONTEXT\ Typesetting Macros,
%D       subtitle=Overloads,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\writestatus{loading}{ConTeXt Typesetting Macros / Overloads}

\unprotect

%D See \LUA\ file for comments. I'll probably never use this code outside the
%D project where it had some experimental use. (Occasionally we do some spell
%D checking and suspicious word usage marking.) So there is not much documentation
%D here. Keep in mind that overloading only makes sense for content that gets
%D replaced as otherwise normal attributes make more sense. Using this otherwise
%D is weird but one never knows what users come up with.

\registerctxluafile{typo-ovl}{}

\definesystemattribute[overloads][public,global]

\installcorenamespace{overloads}

%D Watch how we abuse highlights.

\newcount\c_typo_overload_font_id

\unexpanded\def\typo_overloads_define#1%
  {\begingroup
   % we pack so we avoid interference (and for sure don't process!)
   \setbox\scratchbox\hpack\bgroup
      \global\c_typo_overload_font_id\fontid\font
      \resetallattributes % so we only change what gets set
      \highlight[#1]%
      \signalcharacter
      \global\c_typo_overload_font_id
        \ifnum\c_typo_overload_font_id=\fontid\font
          \zerocount
        \else
          \fontid\font
        \fi
   \egroup
   \global\expandafter\chardef\csname\??overloads#1\endcsname
     \clf_overloadsattribute{#1}\c_typo_overload_font_id\scratchbox
   \endgroup}

\unexpanded\def\setoverloads[#1]%
  {\ifcsname\??overloads#1\endcsname\else
      \typo_overloads_define{#1}%
   \fi
   \attribute\overloadsattribute\csname\??overloads#1\endcsname}

\unexpanded\def\registeroverloads[#1]%
  {\ifcsname\??overloads#1\endcsname\else
      \typo_overloads_define{#1}%
   \fi}

\unexpanded\def\resetoverloads
  {\overloadsattribute\attributeunsetvalue}

%D We hook this into the replacement module, probably the only place where it makes
%D sense. Here is an adapted version of an example:
%D
%D \starttyping
%D \replaceword[basics][new]  [old]
%D \replaceword[basics][now]  [hl3->never]
%D \replaceword[basics][never][now]
%D \replaceword[basics][heck] []
%D
%D \definehighlight[hl1][style={\setbar[underbar]\red\setcharactercasing[WORD]\bf}]
%D \definehighlight[hl2][style={\setbar[overbar]\blue\setcharactercasing[Words]}]
%D \definehighlight[hl3][style={\setbar[overstrike]\green\bs}]
%D
%D \registeroverloads[hl1]
%D \registeroverloads[hl2]
%D \registeroverloads[hl3]
%D
%D \start \setreplacements[basics][hl1] What the heck, it's now or never, isn't it new? \stop \par
%D \start \setreplacements[basics][hl2] What the heck, it's now or never, isn't it new? \stop \par
%D \start \setreplacements[basics][hl1] What the heck, it's now or never, isn't it new? \stop \par
%D \start \setreplacements[basics]      What the heck, it's now or never, isn't it new? \stop \par
%D \stoptyping
%D
%D We used it to mark synonyms that should not be corrected by the editor. Sort of the
%D reverse of not having a word in a vetted wordlist. A bit out of place in a typesetting
%D system. If really needed we can support multiple words seperataed by spaces but I didn't
%D need it. And \unknown\ fonts are supported but at fixed size!

\ifdefined\setreplacements

    \unexpanded\def\setreplacements
       {\dodoubleempty\languages_replacements_set}

    \unexpanded\def\languages_replacements_set[#1][#2]%
      {\clf_setreplacements{#1}%
       \ifsecondargument
         \setoverloads[#2]%
       \else
         \resetoverloads
       \fi}

\else

    % something weird

\fi

\protect