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A complete parser has to be strict. Emacs's syntax-highlighting, as we all know, is very heuristic and approximate. While it does a good job for the common cases, it's easy to break it with more freakish examples. A real compiler can't allow that.

To parse this correctly, the parser has to receive a "TYPE-NAME" token for XX and an "IDENTIFIER" token for yy. If the parser receives an IDENTIFIER token for XX, this will result in a parse error.

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To be more precise, "a context-free parser has to receive a TYPE-NAME token...". A hand-coded parser would be able to parse things just fine if both XX and yy were IDENTIFIERs.

Or, to put it another way, you resort to uglyfying the lexer to overcome definiciencies in the parser.

Indeed, which is exactly the point of the article this discussion refers to

Alternately, you can implement such context-sensitive features in another pass after the parse.

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