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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% Module: Letterspacing Facility
%
% Synopsis: This module provides a fairly comprehensive letterspacing
% facility for ZzTeX.
%
% Author: Paul C. Anagnostopoulos
% Created: 10 July 1997
%
% Copyright 1989--2020 by Paul C. Anagnostopoulos
% under The MIT License (opensource.org/licenses/MIT)
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Letterspacing Commands
% ------------- --------
\defineskip{\zlspamount}{0pt}
\defineskip{\zlspace}{0pt}
\def \letterspace #1#2{% {amount[,space]}{text}
{\zlspparse #1,,\zmark
\zletterspace{#2}}}
\def \eletterspace #1#2{% {amount[,space]}{text}
\edef \znext {\noexpand\letterspace{#1}{#2}}%
\znext}
\def \zlspparse #1,#2,#3\zmark{%
\zlspamount = #1\relax
\if \emptyargp{#2}%
\measurespacewidth{\zlspace}%
\advance \zlspace by \zlspamount
\else
\zlspace = #2\relax
\fi}
% These commands can be used in letterspaced text, but must do nothing
% when letterspacing is not in progress.
\let \lsp = \relax
\let \nolsp = \relax
\def \lspspace {\space}%
\def \zlspoff {\relax}%
\def \lspoff {\zlspoff}%
\def \zlspon {\relax}%
\def \lspon {\zlspon}%
% Letterspacing Engine
% ------------- ------
\def \zletterspace #1{% {text}
\def \lsp {\nobreak\hskip \zlspamount}%
\def \lspspace {\hskip \zlspace}%
\def \zzlspoff {\zlspoff}%
\def \zzlspon {\zlspon}%
\setflag \zlsping = \true
\let \zlspprev = \relax
\setflag \zlspprevchar = \false
\let \zmark = \relax
{\zlspa #1\zmark}}
\def \zlspa {\futurelet\zlspcur \zlspb}
\def \zlspb {%
\let \znext = \zlspc
\if \tokeqlp{\zlspcur}{\zmark}%
\let \znext = \relax
\else\if \cateqlp{\noexpand\zlspcur}{\zspacetoken}%
\if \zlsping \aftergroup\lspspace \else \aftergroup\space \fi
\else\if \cateqlp{\noexpand\zlspcur}{\bgroup}%
\aftergroup{%
\else\if \cateqlp{\noexpand\zlspcur}{\egroup}%
\aftergroup}%
\else\if \tokeqlp{\zlspcur}{\zzlspoff}%
\setflag \zlsping = \false
\else\if \tokeqlp{\zlspcur}{\zzlspon}%
\setflag \zlsping = \true
\else
\let \znext = \zlspd
\fi\fi\fi\fi\fi\fi
\znext}
\def \zlspc {% Discard current token.
\let \zlspprev = \zlspcur
\setflag \zlspprevchar = \false
\afterassignment\zlspa \let\zlspcur = }
\long\def \zlspd #1{% Process current token.
\let \zlspprev = \zlspcur
\if \cateqlp{\noexpand#1}{\relax}%
\setflag \zlspprevchar = \false
\aftergroup#1%
\else\if \cateqlp{\noexpand#1}{\noexpand~}%
\setflag \zlspprevchar = \false
\if \zlsping \aftergroup\lspspace \else \aftergroup\space \fi
\else\if \orp{\andp{\codeeqlp{\zlspprev}{-}}{\codeeqlp{\zlspcur}{-}}}
{\orp{\andp{\codeeqlp{\zlspprev}{`}}{\codeeqlp{\zlspcur}{`}}}
{\andp{\codeeqlp{\zlspprev}{'}}{\codeeqlp{\zlspcur}{'}}}}%
\setflag \zlspprevchar = \true
\aftergroup#1%
\else
\if \andp{\zlspprevchar}{\zlsping}\aftergroup\lsp \fi
\setflag \zlspprevchar = \true
\aftergroup#1%
\fi\fi\fi
\zlspa}
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