m[
      < %          # node 0 -> node 1 ->
      (            # node 0 -> node 1 -> node 2 (?) ->
         %         # node 0 -> node 1 -> node 2 (yes) ->
           (       # node 0 -> node 1 -> node 2 (yes) -> node 4 (?) ->
              [^>] # node 0 -> node 1 -> node 2 (yes) -> node 4 (no) ->
            | [^%] # node 0 -> node 1 -> node 2 (yes) -> node 4 (yes) ->
                   #                                     node 3 (?) ->
           ) 
       | [^%]      # node 0 -> node 1 -> node 2 (no)  -> node 3 (?) ->
      )*           # 
      (%)+         # node 5 (?)
      >            # node 5 (no) -> node 6
    ]x

##</code><code>##

    m[
      < %
      (?:
          [^%]+
        | % [^%>]
      )*
      %*          # I left it as %* so the "insides" can be easily
                  # grouped & captured
      % >
    ]x