 
 CLIENT_SIDE_MODE_LINES = []
 for mode in ['md', 'html', 'coffeescript', 'javascript']
-    for s in ['', '(hide=false)', '(hide=true)']
+    for s in ['', '(hide=false)', '(hide=true)', '(once=false)']
         CLIENT_SIDE_MODE_LINES.push("%#{mode}#{s}")
 
 # Return true if there are currently unsynchronized changes, e.g., due to the network

        cm = @codemirror
        block = opts.block

        console.log("execute_cell_client_side: block='#{cm.getRange({line:block.start,ch:0}, {line:block.end+1,ch:0})}'")

        # get the input text -- after the mode line
        input = cm.getRange({line:block.start+1,ch:0}, {line:block.end+1,ch:0})
        i = input.indexOf(MARKERS.output)


        # update so that client sees rendering
        @process_sage_updates()

    split_cell_at: (pos) =>
        # Split the cell at the given pos.
