2.2 Comments

A comment may be introduced at almost any point in a T3X program using an exclamation point (!). It extends up to but not including the end of the current line. Therefore, a comment is treated the same way as a single white space character, and consequently,

wh! this is a comment
ile(1) ;

is equal to

wh ile(1) ;

and not to

while(1) ;

Therefore, comments may not occur inside of a single token, but only between two tokens. This is particularly valid for string literals and character literals which are single tokens as well. A ! character inside one of these literals is treated like an ordinary character.