attach/attachPane.js
function (kb, subject) {
      if (kb.updater.editable(subject.doc(), kb)) return subject.doc()
      var store = kb.any(subject.doc(), QU('annotationStore'))
      return store
    }
function (kb, subject) {
      if (kb.updater.editable(subject.doc(), kb)) return subject.doc()
      var store = kb.any(subject.doc(), QU('annotationStore'))
      return store
    }
Where can we write about this thing?  Returns term for document or null