code: public static boolean isValid(final String cssValue) {
          String trimmedCssValue = null;
          if (cssValue == null) {
              return false;
          } else if ((trimmedCssValue = StringUtil.strip(cssValue))
                  .equalsIgnoreCase(INITIAL)
                  || trimmedCssValue.equalsIgnoreCase(INHERIT)
                  || trimmedCssValue.equalsIgnoreCase(NONE)) {
              return true;
          } else if (trimmedCssValue.toLowerCase().startsWith("url(")
                  && trimmedCssValue.endsWith(")")) {
              return true;
          }
          return false;
      }
docs: To check whether the given {@code cssValue} is valid for this class.
  
  @param cssValue
  @return true if the given {@code cssValue} is valid for this class.
  @since 1.0.0
  @author WFF