/** Given a .message-row element, this function returns whethe the
        current user may, at least hypothetically, delete the message
        globally.  A user may always delete a local copy of a
        post. The server may trump this, e.g. if the login has been
        cancelled after this page was loaded.
    */
    cs.userMayDelete = function(eMsg){
      return +eMsg.dataset.msgid>0
        && (this.me === eMsg.dataset.xfrom
            || F.user.isAdmin/*will be confirmed server-side*/);
    };

    /** Returns a new Error() object encapsulating state from the given
        fetch() response promise. */
    cs._newResponseError = function(response){

        id = e.dataset.msgid;
      }else{
        e = this.getMessageElemById(id);
      }
      if(!(e instanceof HTMLElement)) return;
      if(this.userMayDelete(e)){
        this.ajaxStart();
        fetch("chat-delete/" + id)
          .then(function(response){
            if(!response.ok) throw cs._newResponseError(response);
            return response;
          })
          .then(()=>this.deleteMessageElem(e))
          .catch(err=>this.reportErrorAsMessage(err))
          .finally(()=>this.ajaxEnd());
      }else{
        this.deleteMessageElem(id);
      }
    };