A regular expression included in a search request must be quoted and must begin with ##. Examples:

Apple and "##199[0-9]"
Apple and "##19[0-9]+"

A regular expression must match a single whole word. For example, you could not search for "apple pie" with a regular expression "##app.*ie". 

For information on the regular expression syntax, see Regular Expressions. A regular expression is like the * wildcard character in its effect on search speed: the closer to the front of a word the expression is, the more it will slow searching. "Appl*" will be nearly as fast as "Apple", while "*pple" will be much slower.

Search Features