Changed isAllowed with userCan, but it seems like the page is a bit overly protective as a blocked user can't see the content at all. Perhaps its only my setup?

Approx idea for permissions/protections is that page protection and user blocking forms a lower bound on protecting page content with "userCan", and a more fine grained permission is built on top of that with "isAllowed". For now individual calls to content changing calls to the API is guarded, but later individual fields could be protected if necessary.

Blocked users should be able to read, unless the wiki is private (reading is not allowed for anons) and wgBlockDisablesLogin is set.

Please compare the behavior for item pages to the behavior for wikitext pages. It should be the same wrt blocking/protection.

Note: ItemViewAction needs to return false from requiresUnblock(), otherwise blocked users can't view. Maybe ItemViewAction should just extend ViewAction? Will look at this in the context of bug 37682.

Created attachment 10796
Screendump showing the effect of the block message on the page display.

Attached:

Changes in patchset https://gerrit.wikimedia.org/r/#/c/12907/

Write tests for this.