>=0 ==> SUCCESS -1 ==> CONNECTION_FAILED -2 ==> DOCUMENT_ALREADY_LOADED -3 ==> DOCUMENT_DOES_NOT_EXIST -4 ==> EDITING_OUTSIDE_BOUNDS -5 ==> CANNOT_EDIT_MULTIPLE_LINES -6 ==> CANNOT_LOCK -7 ==> CANNOT_UNLOCK -8 ==> LINE_DOES_NOT_EXIST