+% Output a mark which sets \thischapter, \thissection and \thiscolor.
+% We dump everything together because we only have one kind of mark.
+% This works because we only use \botmark / \topmark, not \firstmark.
+%
+% A mark contains a subexpression of the \ifcase ... \fi construct.
+% \get*marks macros below extract the needed part using \ifcase.
+%
+% Another complication is to let the user choose whether \thischapter
+% (\thissection) refers to the chapter (section) in effect at the top
+% of a page, or that at the bottom of a page. The solution is
+% described on page 260 of The TeXbook. It involves outputting two
+% marks for the sectioning macros, one before the section break, and
+% one after. I won't pretend I can describe this better than DEK...
+\def\domark{%
+ \toks0=\expandafter{\lastchapterdefs}%
+ \toks2=\expandafter{\lastsectiondefs}%
+ \toks4=\expandafter{\prevchapterdefs}%
+ \toks6=\expandafter{\prevsectiondefs}%
+ \toks8=\expandafter{\lastcolordefs}%
+ \mark{%
+ \the\toks0 \the\toks2
+ \noexpand\or \the\toks4 \the\toks6
+ \noexpand\else \the\toks8
+ }%
+}
+% \topmark doesn't work for the very first chapter (after the title
+% page or the contents), so we use \firstmark there -- this gets us
+% the mark with the chapter defs, unless the user sneaks in, e.g.,
+% @setcolor (or @url, or @link, etc.) between @contents and the very
+% first @chapter.
+\def\gettopheadingmarks{%
+ \ifcase0\topmark\fi
+ \ifx\thischapter\empty \ifcase0\firstmark\fi \fi
+}
+\def\getbottomheadingmarks{\ifcase1\botmark\fi}
+\def\getcolormarks{\ifcase2\topmark\fi}
+
+% Avoid "undefined control sequence" errors.
+\def\lastchapterdefs{}
+\def\lastsectiondefs{}
+\def\prevchapterdefs{}
+\def\prevsectiondefs{}
+\def\lastcolordefs{}
+