Info Catalog
as: RX-Syntax
9.39.5.1 Special Characters
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The presence of a ';' appearing anywhere on a line indicates the start
of a comment that extends to the end of that line.
If a '#' appears as the first character of a line then the whole line
is treated as a comment, but in this case the line can also be a logical
line number directive (
Comments) or a preprocessor control
command (Preprocessing).
The '!' character can be used to separate statements on the same
line.