2.1.1 [PageVisibility] 4.2 Extensions to the Document interface

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V0001:

The specification states: 

 4.2 Extensions to the Document interface
 ...
 visibilityState attribute
  
 On getting, visibilityState attribute MUST return one of the following DOMStrings
 or a vendor prefixed DOMString as defined in 4.5 Vendor Prefixes:

    ▪ hidden,
    ▪ visible,
    ▪ prerender,
    ▪ unloaded.

IE10 Mode (All Versions)

            prerender and unloaded are not supported.

IE11 Mode (All Versions)

unloaded is not supported.