Does the control symbol obtained by following the escape character by return (\<return>, catcode 0 then catcode 5) behave like the control space character (\<space>, catcode 0 then catcode 10)? It seems to:
\TeX\ blah
typesets the same way
\TeX\
blah
does. But I can't justify this behavior by tracing through the lexing process as described in the texbook. What exactly is tex doing here?
There's this in plain.tex
\def\^^M{\ } % control <return> = control <space>
\def\^^I{\ } % same for <tab>
\def\^^M{something else} and see the results.
Commented
Dec 1, 2017 at 18:54
\<nonletter> being lexed to the same control symbol other than <nonletter> = <return>, <space>, <tab>?
\!, \,, etc. you mean if there's another case in which two non-letters end up expanding to the same thing? I don't think there's any other case, but you could do \def\.{\,} and \. would end up expanding to the same as \,. I'm not sure I understand what you are asking.
\<return> and \<tab> to expand to \<space>. It's as if he defined \def\a{\ } \def\b{\ } \def\c{\ } all three macros \a, \b, \c, would expand to \ but by no means it's “natural”.
\let\^^M=\ % ... plain.tex is usually so careful about conserving memory.
\endlinecharis added, so what TeX sees is<backslash><endlinechar>.