                     handler.error(err)
                     return
                 if mesg.done
-                    # special internal cocalc message.
+                    # done is a special internal cocalc message.
                     handler.done()
                     return
                 if mesg.msg_type == 'clear_output'


        @ensure_backend_kernel_setup()

        cell   = @store.get('cells').get(id)
        input  = (cell.get('input') ? '').trim()

        @_running_cells ?= {}


        handler = @_output_handler(cell)

        handler.on 'change', (save) =>
            if not @store.getIn(['cells', id])
                # The cell was deleted, but we just got some output
                # NOTE: client shouldn't allow deleting running or queued
                # cells, but we still want to do something useful/sensible.
                # We put cell back where it was with same input.
                cell.input = orig_cell.get('input')
                cell.pos   = orig_cell.get('pos')
            @syncdb.set(cell, save)

        handler.once 'done', =>
