A regular expression pattern is a template that matches a set of text strings.

A regular expression is a string comprised of normal or literal characters and special meta-characters. The normal characters match themselves, while the special characters define repetition, character classes, backreferences to prior matching fragments, etc…

While a complete discussion of regular expressions is beyond the scope of these Help Pages, an in depth reference of EASA's regular expression pattern language, is found in the Java documentation below:

https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html