I would like to extract this second case from #397 to this separate issue, so that we can discuss both cases separately.

E           textx.exceptions.TextXSyntaxError: None:5:10: Expected Not or '.' or '
E           ' or '>>>' => ' COMMENT: *'

The Not part is not self-explanatory. Would it be possible to complement the Not with an expansion of what exactly should not be present? I am not sure about the exact way of how this should look like: this could be an expansion as, for example, Not(GrammarTerm) where GrammarTerm is an identifier in the grammar file, or, if this not possible, even expanding to the actual regular expression: Not (/.../).

I am curious to know if either or both of these features would be doable with not much effort. Thank you.