code: public static boolean isRectValue (@Nullable final String sCSSValue)
    {
      final String sRealValue = StringHelper.trim (sCSSValue);
      if (StringHelper.hasText (sRealValue))
      {
        // Current syntax: rect(a,b,c,d)
        if (RegExHelper.stringMatchesPattern (PATTERN_CURRENT_SYNTAX, sRealValue))
          return true;
  
        // Backward compatible syntax: rect(a b c d)
        if (RegExHelper.stringMatchesPattern (PATTERN_OLD_SYNTAX, sRealValue))
          return true;
      }
      return false;
    }
docs: Check if the passed value is CSS rectangle definition or not. It checks
  both the current syntax (<code>rect(a,b,c,d)</code>) and the old syntax (
  <code>rect(a b c d)</code>).
  
  @param sCSSValue
  The value to check. May be <code>null</code>.
  @return <code>true</code> if the passed value is a rect value,
  <code>false</code> if not