That position number is needed in case the node has siblings of the same type and name, to indicate which one we're referring to.

位置号是必需的，以防节点有相同类型和名称的兄弟节点，这样可以表明我们引用的是哪个节点。

youdao

When you have multiple siblings with the same name, you can disambiguate the sibling you want by using the index notation.

当有同名的多个同级节点时，可以用下标区分出想要的同级节点。

youdao