Function getZLevelTop

packages/core/src/document/node/node.ts:769–782

(child: Node, zLevel: number)

 * get the top node of the same zLevel
 */
export const getZLevelTop = (child: Node, zLevel: number): Node | null => {
  let l = child.zLevel
  if (l < zLevel || zLevel < 0) {
    return null
  }
  if (l === zLevel) {
    return child
  }
  let r: any = child
  while (r && l-- > zLevel) {
    r = r.parent
  }
  return r
}

/**
 * check if node1 contains node2