Added Limitations section

docs/hooks/hook_civicrm_permission_check.md

@@ -28,6 +28,12 @@ and above.
 
 -   null
 
+## Limitations
+
+-   This hook is implemented for forms (eg Add, Edit) but not yet for
+    reports and viewing of objects like Activities on the Contact
+    Summary page as of 4.7.17
+
 ## Examples
 
 The following is an excerpt from [the CiviCRM Multisite
@@ -81,4 +87,4 @@ not detailed in full.
 
     function _eventmgmt_isEventMgr() {
       //determine if the logged in user should be granted access to this particular event's participant listing page (i.e. they are an "event manager")
-    }
+    }
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