code: public WikiFormat switchStyle(WikiStyle wikiStyle)
      {
          WikiFormat clone = getClone();
          if (clone.fStyles.contains(wikiStyle)) {
              clone.fStyles.remove(wikiStyle);
          } else {
              clone.fStyles.add(wikiStyle);
          }
          return clone;
      }
docs: Creates a new format object where the specified style is switched: if
  this format contains the given style then the resulting format does not
  and vice versa.
  
  @param wikiStyle the style to switch
  @return a format object where the given style is inverted relatively to
  this format