Add a client-side function odata.matchesPattern (to align with term Validation.Pattern) that can be used within the Apply dynamic expression. It takes two arguments of type Edm.String and returns true if the first argument matches the regular expression in the second argument, using syntax and semantics of ECMA 262 (JavaScript) regular expressions, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions