code: public static boolean isValid(final String cssValue) {
          final String trimmedCssValue = TagStringUtil
                  .toLowerCase(StringUtil.strip(cssValue));
  
          if (StringUtil.containsSpace(trimmedCssValue)) {
              return false;
          }
  
          if (CssLengthUtil.getLengthValueAsPremitiveAndUnit(
                  trimmedCssValue).length == 2) {
              return true;
          }
  
          return PREDEFINED_CONSTANTS.contains(trimmedCssValue);
      }
docs: validates if the given cssValue is valid for this class.
  
  @param cssValue
  the value to check.
  @return true if valid and false if invalid.
  @author WFF
  @since 1.0.0