manifest
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
The manifest attribute of the <html> element specifies a URL of an application cache manifest that is downloaded in the early stages of page load.
Note: manifest-based caching mechanism has been deprecated. Use service workers instead.
The manifest attribute has only effect during early stages of page load, thus changing it via regular DOM interfaces has no effect, Window.applicationCache interface instead.
Browser compatibility
BCD tables only load in the browser