code: public void addDeclaration(Element el, PseudoElementType pseudo, Declaration decl)
      {
          List<Declaration> list = getOrCreate(el, pseudo);
          list.add(decl);
      }
docs: Adds a declaration for a specified list. If the list does not exist yet, it is created.
  @param el the element that the declaration belongs to
  @param pseudo an optional pseudo-element or null
  @param decl the new declaration