Regular expression can be used in filters and find/$match operators. Regular expressions are evaluated using java, so will conform to the rules:
A regular expression, or regex, is a sequence of characters that specifies a pattern which can be searched for in a text. A regex defines a set of strings, usually united for a given purpose. Suppose you need a way to formalize and refer to all the strings that make up the format of an email address. Since there are a near infinite number of possible email addresses, it’d be hard to enumerate them all. However, as we know an email address has a specific structure, and we can encode that using the regex syntax.
A regex processor translates a regular expression into an internal representation which can be executed and matched against the text being searched. It will tell you whether a string is in the set of strings defined by a pattern or find a substring that belongs in that set.
Example in CLI
Using java.util.regex.Pattern in the API: