code: public static ByStrictClassName strictClassName(final String className) {
          if (className == null)
              throw new IllegalArgumentException(
                      "Cannot find elements when the class name expression is null.");
  
          if (className.matches(".*\\s+.*")) {
              throw new InvalidSelectorException(
                      "Compound class names are not supported. Consider searching for one class name and filtering the results.");
          }
  
          return new ByStrictClassName(className);
      }
docs: Finds elements based on the value of the "class" attribute.
  If the second param is set to true, if an element has many classes then
  this will match against each of them. For example if the value is "one two onone",
  then the following "className"s will match: "one" and "two"
  
  @param className The value of the "class" attribute to search for
  @return a By which locates elements by the value of the "class" attribute.