requests started using the XMLHttpRequest object or fetch() API object-subrequest —— 插件的请求,比如Flash subdocument 可以指定的类型选项: ~script, ~image, ~stylesheet, ~object, ~xmlhttprequest, ~object-subrequest, ~subdocument,
To specify a field within a subdocument, use dot notation. limit number Optional. To specify a field within a subdocument, usedot notation. uniqueDocs Boolean Optional.
to the document root, otherwise it relates to the currently evaluated document, which is possibly a subdocument