This screenshot is token from the book Ullman,
How can following be a lexical error? because "elipseSize" should have a token recorded as an identifier.
author is clearly saying "the use of identifier elipseSize" that means it detected as identifier already.
But I also don't have a good reason why it is a lexical error, but Lexical analyzer also use symbol table while processing and I think some DFA also, so maybe by the help of DFA it will recognize that something is a valid token or not and so misspell of id, keyword will become a lexical error.[not so sure]
its really great thanks