2.2.35 [W3C-HTML51] Section 6.6.1 The session history of browsing contexts

C0050: Document objects are discarded based on content expiration, disk space usage, and preferences for content storage

The specification states:

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     ...
     User agents may discard the Document objects of entries other than the current entry 
     that are not referenced from any script, reloading the pages afresh when the user or 
     script navigates back to such pages. This specification does not specify when user 
     agents should discard Document objects and when they should cache them.

EdgeHTML Mode

Document objects are discarded based on content expiration, disk space usage, and preferences for content storage.