Invalid pattern.

Additional Information

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 lookahead not.
    or
'X' positional patterns may appear only at the 'Y' of a compound pattern.
    or 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.

Recovery

Compilation continues but no compiled source code file will be saved.

Explanation

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-end line-start, so such a pattern is not accepted.

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