Possible empty pattern encountered.
#2516 Compile-time warning
Possible empty pattern encountered.
Additional Information
This pattern can match zero characters, and therefore slow the program
down.
or
A sub-pattern in a repetition might repeat without matching any characters.
Explanation
As of Version 2 Release 4, OmniMark now allows patterns in find and
translate rules to match zero characters. This is most useful
for moving from one group to another in find rules without
actually consuming characters.
Note that if a find rule matches no characters, the next
successful find rule must match at least one character. This
prevents unexpected looping.
The second type of message can occur when a sub-pattern of the form
(A? B* lookahead not C)+ is
encountered (or a similar combination thereof).