While it is assumed that the reader is familiar with regular expressions, it is useful to review. This will ensure that the terminology is understood, and it may encourage you to use features that you've not been using.
Like shell patterns, regular expressions match on a character-by-character basis unless a meta-character is encountered in the pattern. Regular expressions have more meta-characters than shell patterns, which makes them more powerful. It also makes them more difficult to master.
When searching for text within a file, it is often necessary to use anchors. An anchor is a meta-character that can cause a pattern to be attached to another entity. Regular expressions define two anchors: