Nice to know the \s tip.
That said, I tested to write something like remove in a new line of a batch file, and Scintilla's Lexer doesn't highlight it as comment.

In fact, seeking in [LexOthers.ccx@l146](https://github.com/geany/geany/blob/master/scintilla/lexers/LexOthers.cxx#L146) it seems the rem keyword for comments is in fact hard-coded, so comment_single parameter is useless (verified just now)

This is a Scintilla problem, though, but I also learned that the Lexer seeks for a complete word, so no problem with not specifying the space after rem, in anticipation of the day this Lexer will maybe be modified to take into account the comment_single parameter.