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.

PermittedInt() returns true if a value is in a list of permitted integers.

Use the regexp.MustCompile() function to parse a regular expression pattern for sanity checking the format of an email address.

Add a new NonFieldErrors []string field to the struct, which we will use to hold any validation errors which are not related to a specific form field(Like "email or password is incorrect").