code: public static boolean isValid(final String cssValue) {
          final String trimmedCssValue = TagStringUtil
                  .toLowerCase(StringUtil.strip(cssValue));
          if (StringUtil.containsSpace(trimmedCssValue)) {
              return false;
          }
          try {
              final int parsedValue = Integer.parseInt(trimmedCssValue);
  
              return !(parsedValue == 0
                      && (StringUtil.containsMinus(trimmedCssValue)
                              || StringUtil.containsPlus(trimmedCssValue)));
          } catch (final NumberFormatException e) {
          }
  
          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