-% @math means output in math mode.
-% We don't use $'s directly in the definition of \math because control
-% sequences like \math are expanded when the toc file is written. Then,
-% we read the toc file back, the $'s will be normal characters (as they
-% should be, according to the definition of Texinfo). So we must use a
-% control sequence to switch into and out of math mode.
-%
-% This isn't quite enough for @math to work properly in indices, but it
-% seems unlikely it will ever be needed there.
+% @math outputs its argument in math mode.
+% We don't use $'s directly in the definition of \math because we need
+% to set catcodes according to plain TeX first, to allow for subscripts,
+% superscripts, special math chars, etc.
+%
+% @math does not do math typesetting in section titles, index
+% entries, and other such contexts where the catcodes are set before
+% @math gets a chance to work. This could perhaps be fixed, but for now
+% at least we can have real math in the main text, where it's needed most.