signature" letters (which optionally is terminated by another colon `:`),
and the remainder is the pattern to match against the path.
The "magic signature" consists of ASCII symbols that are neither
-alphanumeric, glob, regex special charaters nor colon.
+alphanumeric, glob, regex special characters nor colon.
The optional colon that terminates the "magic signature" can be
omitted if the pattern begins with a character that does not belong to
"magic signature" symbol set and is not a colon.