Can't have only LOOKAHEAD inside a '*' or a '+'.
or Can't save text inside a LOOKAHEAD, '*', or '+'.
or Consecutive 'X' subpatterns must be separated by parentheses. The last
'X' subpattern is followed by 'Y'.
where X is lookahead or lookaheadnot.
or 'X' positional patterns may appear only at the 'Y' of a compound
where X is content-end, content-start,
value-end, or value-start, and Y is 'end' or 'start'.
or Only 'X' positional patterns can directly precede 'Y'.
or Only 'X' positional patterns can directly follow 'Y'.
or Only one EXCEPT is allowed in a character set.
or The positional pattern 'X' is not allowed in the current pattern.
Compilation continues but no compiled source code file will be saved.
These messages are given for patterns which either are not
supported by the language or are impossible to match. For example,
nothing can match word-endline-start, so such a
pattern is not accepted.