[cl-ppcre-devel] Roles of scanner vs. parser vs. lexer?

Hi everybody, I've been reading the CL-PPCRE docs and code to get a clear specification of the syntax. Ultimately I'd like to add syntax highlighting for CL-PPCRE regexps to the Climacs text editor. But there seems to be a certain amount of defensive or sloppy programming (things being done in more than one place). The scanner knows something about skipping # comments but the lexer does too. The lexer has code to ignore \E markers but I get the impression the scanner removes them before the lexer starts. If this kind of duplication does exist, is there a useful reason for it? -- Derek