containsNode (node) {
    if (this === node) {
      return true
    }

    const childs = this.childs
    if (childs) {
      // TODO: use the js5 Array.some() here?
      for (let i = 0, iMax = childs.length; i < iMax; i++) {
        if (childs[i].containsNode(node)) {
          return true
        }
      }
    }

    return false
  }
Check if given node is a child. The method will check recursively to find
this node.
@param {Node} node
@return {boolean} containsNode