code: private Directive createDirective(
              final String name,
              final String value,
              final List<Parameter> params) {
          if (isQuoted(value)) {
              return new QuotedDirective(name, value, params);
          }
          if (HeaderConstants.LINK_HEADER.equals(name)) {
              return new LinkDirective(value, params);
          }
          return new Directive(name, value, params);
      }
docs: Creates a header element.
  Called from {@link #parseDirective}.
  
  @return a header element representing the argument