code: public static Validator<CharSequence> regex(@NonNull final CharSequence errorMessage,
                                                  @NonNull final Pattern regex) {
          return new RegexValidator(errorMessage, regex);
      }
docs: Creates and returns a validator, which allows to validate texts to ensure, that they match a
  certain regular expression.
  
  @param errorMessage
  The error message, which should be shown, if the validation fails, as an instance of
  the type {@link CharSequence}. The error message may not be null
  @param regex
  The regular expression, which should be used to validate the texts, as an instance of
  the class {@link Pattern}. The regular expression may not be null
  @return The validator, which has been created, as an instance of the type {@link Validator}