Matches() returns true if a value matches a provided compiled regular expression pattern.

MaxChars() returns true if a value contains no more than n characters.

MinChars() returns true if a value contains at least n characters.

NotBlank() returns true if a value is not an empty string.

PermittedValue() returns true if a value is in a list of specific permitted values.

Define a new Validator struct which contains a map of validation error messages for our form fields.