code: function doVisitFull(visit, node) {
    if(node.left) {
      var v = doVisitFull(visit, node.left)
      if(v) { return v }
    }
    var v = visit(node.key, node.value)
    if(v) { return v }
    if(node.right) {
      return doVisitFull(visit, node.right)
    }
  }
docs: Visit all nodes inorder