Regular Expression Operator

The value in a field can be evaluated using a regular expression. The regular expression operator has the following modes: 
MATCH:regex
CONTAIN:regex
where:
regex
is the regular expression.

MATCH mode

MATCH returns true if the regular expression matches the entire field.

In this example, the value would match 4 digits followed by a dash followed by four more digits. Anything else would fail the value check. 
Value in {MATCH: [0-9]{4}-[0-9]{4}}

For example, 1234-2345 would pass and 1234-12345 would not.

CONTAIN mode

CONTAIN returns true if the regular expression matches at least one sub-string.

In this example, the value would match 4 digits followed by a dash followed by four more digits. Anything else would fail the value check. 
Value in {CONTAIN: [0-9]{4}-[0-9]{4}}

Given the same example, both 1234-2345 and 1234-12345 would pass because they have at least one sub-string that matches the regular expression.