Due to the wide variety of menu screen formats, this property can be used to tune the parsing for a specific menu screen (or group matching the recognition criteria).
Regular Expressions are well documented on the Web, and a search on "regular expression tutorial" can provide some help if you are interested in learning more.
To help narrow-down your understanding of the type of regular expression used to parse menu screens, we have used a "Match" regular expression type, and we have matched not the whole menu option but just the option identifier text.
Here is a description for the default regular expresssion: