Two editmarkers that should always follow exact formats (per CollaborationHubContentHandler::onParserOutputPostCacheTransform):

• <ext:ck:editmarker ...> for the edit and action buttons in general (edit section, sign up, create feature, whatever)
• <ext:ck:missingfeature-note ...> for the missing page info string we put on hubs for included features that don't yet exist

Need to add tests to loudly verify nothing messes them up, since if the regex just starts not matching, that's a not terribly noticeable failure on its own.