This question already has an answer here:
I know that plain TeX is the low-level typographical language that describes nearly every aspect of presentation, taking care of things like paragraph breaks, new pages, and the like.
I know (well, I've inferred) that LaTeX is in fact written in TeX, partly to demonstrate its power and partly for sheer convenience; LaTeX allows the author to construct documents logically rather than 'typographically' as using plain TeX, no-frills, would have you do.
What I don't know is how LaTeX really does it. Does LaTeX compile the document into a PDF, or does it compile the document into plain TeX for tex
to actually process? What features does LaTeX actually add on to plain TeX?
\def
or\newcommand
that you may put in your document. – David Carlisle Apr 30 '13 at 11:24\begin
is a macro written in TeX just like the rest of latex \def\begin#1{% \@ifundefined{#1}% {\def\reserved@a{\@latex@error{Environment #1 undefined}\@eha}}% {\def\reserved@a{\def\@currenvir{#1}% \edef\@currenvline{\on@line}% \csname #1\endcsname}}% \@ignorefalse \begingroup\@endpefalse\reserved@a} – David Carlisle Apr 30 '13 at 12:35