Google Message Security for Google Apps Administration Guide - Manual (Page 225)

Content Manager 225
Range Limitations:
Content Manager does not support the following types of ranges, because they
could cause delays in processing your email:
• Ranges more than {0,25}
• A valid range: (a|b|c){0,10}
• An invalid range: (a|b|c){0,26}
• An invalid range (equivalent to a * ): (a|b|c){1,}
• Nested ranges
• A valid range: (a|b|c){5,10}
• An invalid range: ((a|b|c){0,5}){5,20}
• An invalid range: ((a|b|c){0,5})?
Examples of Regular Expressions
The following examples illustrate the use and construction of simple regular
expressions. Each example includes the type of text to match, one or more
regular expressions that match that text, and notes that explain the use of the
special characters and formatting.
Important: If you create your own regular expression, use the built-in regex tester
to verify that your expression will catch the text you expect and that you haven’t
created an overly general expression.