`cei:class` added in EditMOM3 is not valid

Created by: GVogeler

error message with http://monasterium.net/mom/0ca43e3e-f377-4bd6-a6b3-672bc9d89006/74c26cdb-8e12-41ac-84ac-9dad63cccefc/edit :

invalid tag: class. possible tags are: Abstract (abstract), issued (issued), witnessOrig (witnessOrig), Other textual witnesses (witListPar), Diplomatic Analysis (diplomaticAnalysis), language (lang_MOM)