Exclusive repeat match

This was raised as a problem in the mailing list. The requirement was to match >> and to exclude >>>. Most solutions would find the first two chevrons, or the last two, so in both cases >>> would be found. The actual character matched is unimportant: we will use x to denote it, but remember that certain characters must be escaped in text strings.

Search ( ~"x" .) @0 "xx" ~"x"

This breaks down to
(~"x" .) if first character isn't "x" then match it (to advance the search pointer)
@0 set mark @0 so that the actual match starts here and the preceding character is not coloured in LoF
"xx" literal string to match
next character should not be "x" for match to succeed