code: public Rule SetextHeading1() {
          return Sequence(
                  SetextInline(), push(new HeaderNode(1, popAsNode(), true)),
                  ZeroOrMore(SetextInline(), addAsChild()),
                  wrapInAnchor(),
                  Sp(), Newline(), NOrMore('=', 3), Sp(), Newline()
          );
      }
docs: vsch: #186 add isSetext flag to header node to distinguish header types