Regular Expression Reserved Characters
'Reserved characters' are the regular expression wild card operators themselves. If you have a search or replace string that uses these as actual characters and not a regular expression operator you must make them literal by proceeding them with a \ character.
For search expressions the characters are: - + * ? ( ) [ ] \ | $ ^ !
For replace expressions the characters are: % \ < >
For example, to search for the \ character, you must use a double it - \\ - in order for \ to be matched correctly. If you want to use the < character in a replacement expression, enter \<.
Note: As you become experienced you may discover that % < > need not always be made literal in a replace expression. The critical rule is that if they are directly adjacent to a %n replacement operator they must be made literal with the \ character.
For more information see Search and Replace Regular Expressions.