on.keychord_press = function(chord, key)
	print('key press', chord)
	if Global_state.thread and chord == 'C-o' then
		quit_all_editors(Global_state.thread)
		Global_state.thread = nil
		reset_viewport()
		A()
	elseif chord == 'C-=' then
		-- zoom in
		Viewport.zoom = Viewport.zoom+0.1
		A()
	elseif chord == 'C--' then
		-- zoom out
		if (Viewport.zoom-0.1)*20 >= 1 then  -- disallow font size of 0
			Viewport.zoom = Viewport.zoom-0.1
			A()
		end
	elseif chord == 'C-0' then
		-- reset zoom
		Viewport.zoom = 1.0
		A()
	elseif Cursor_node and Cursor_node.editor.cursor_x then
		local old_top = {line=Cursor_node.editor.screen_top1.line, pos=Cursor_node.editor.screen_top1.pos}
		edit.keychord_press(Cursor_node.editor, chord, key)
		pan_viewport_to_contain_cursor(Cursor_node)
		if chord == 'return' then
			A()
		else
			B()
		end
	else
		if chord == 'up' then
			Viewport.y = math.max(
				Viewport_bounds.ymin,
				Viewport.y - scale(20))
			B()
		elseif chord == 'down' then
			Viewport.y = math.min(
				math.max(
					Viewport_bounds.ymin,
					Viewport_bounds.ymax - App.screen.width/2/Viewport.zoom),  -- conservative; unclear why removing the '/2' makes the bottom inaccessible
				Viewport.y + scale(20))
			B()
		elseif chord == 'left' then
			Viewport.x = math.max(
				Viewport_bounds.xmin,
				Viewport.x - scale(50))
			B()
		elseif chord == 'right' then
			Viewport.x = math.min(
				math.max(Viewport_bounds.xmin, Viewport_bounds.xmax - App.screen.width/Viewport.zoom),
				Viewport.x + scale(50))
			B()
		elseif chord == 'pageup' or chord == 'S-up' then
			Viewport.y = math.max(Viewport_bounds.ymin, Viewport.y - App.screen.height/Viewport.zoom)
			B()
		elseif chord == 'pagedown' or chord == 'S-down' then
			Viewport.y = math.min(
				math.max(
					Viewport_bounds.ymin,
					Viewport_bounds.ymax - App.screen.width/2/Viewport.zoom),  -- conservative; unclear why removing the '/2' makes the bottom inaccessible
				Viewport.y + App.screen.height/Viewport.zoom)
			B()
		elseif chord == 'S-left' then
			Viewport.x = math.max(Viewport_bounds.xmin, Viewport.x - App.screen.width/Viewport.zoom)
			B()
		elseif chord == 'S-right' then
			Viewport.x = math.min(
				math.max(
					Viewport_bounds.xmin,
					Viewport_bounds.xmax - App.screen.width/Viewport.zoom),
				Viewport.x + App.screen.width/Viewport.zoom)
			B()
		end
	end
end