code: public CharSequence matchesPattern(final CharSequence input, final String pattern) {
          if (!Pattern.matches(pattern, input)) {
              fail(String.format(DEFAULT_MATCHES_PATTERN_EX, input, pattern));
          }
          return input;
      }
docs: <p>Validate that the specified argument character sequence matches the specified regular expression pattern; otherwise throwing an exception.</p>
  <pre>Validate.matchesPattern("hi", "[a-z]*");</pre>
  <p>The syntax of the pattern is the one used in the {@link java.util.regex.Pattern} class.</p>
  
  @param input
  the character sequence to validate, not null
  @param pattern
  the regular expression pattern, not null
  
  @return the input
  
  @throws IllegalArgumentValidationException
  if the character sequence does not match the pattern
  @see #matchesPattern(CharSequence, String, String, Object...)