The '[!^13]{1,}' is a wildcard expression (you'll see that I have '.MatchWildcards = True'). The [] tells Word to find any of the enclosed character(s). In this case, the '!' says it's a character
other than what follows. The '^13' represents a paragraph break. The {1,} says there is at least one, such character, but we don't necessarily know what the upper limit is. So Word is being told to find 'Procedure Step:' followed by any number of chracters other than a paragraph break.
Wildcard expressions greatly enhance Word's Find/Replace capacity. See:
http://word.mvps.org/FAQs/General/UsingWildcards.htm
FWIW, you don't even need the macro in this case - it's doing nothing more than you can do through the Find/Replace dialogue.