function createOverlay(desc)
		{
			var overlay = new mxCellOverlay(desc.image || graph.warningImage,
				desc.tooltip, desc.align, desc.valign, desc.offset);

			// Installs a handler for clicks on the overlay
			overlay.addListener(mxEvent.CLICK, function(sender, evt)
			{
				editorUi.alert(desc.tooltip);
			});
			
			return overlay;
		}
Update plugin. Use updateUrl and updateInterval (optional, default is 60000ms)
in the meta data of the diagram to configure the plugin. (Alternatively, the
update-url and update-interval URL parameters may be used instead.)

It will send the XML of the current page to the given URL as a POST request
(with a parameter called xml) and allows for the following type of XML response
(with CORS headers):

<updates>
<update ...>
<model>...</model>
<view ...>
<fit ...>
</updates>

The outermost updates node may contain an optional url and interval property
to change the current updateUrl and updateInterval.

Where update must contain an id attribute to reference the cell in the diagram.

- An optional value attribute that contains XML markup is used as the value for
the cell, with label and tooltip for the label and tooltip, respectively.
Additionally, placeholders="1" can be used to enable placeholders in the label
or tooltip of the cell.

Example: <object label="Hello, %var1%!" var1="World" tooltip=
		"Click <a href=\"https://www.draw.io\">here</a>" placeholders="1">

- An optional replace-value attribute that contains 1 can be specified to
replace the value of the cell. Default is to add the attributes of the XML
value specified above to the existing value of the cell. (Attributes with
an empty string value are removed.)

- An optional style attribute that contains the cell style is used to replace
the existing cell style.

Example: fillColor=red;gradientColor=white;"

- An optional icon attribute that contains JSON is used to add an icon to the
given cell. The object value that the icon attribute is parsed and may contain
a tooltip (string), align ("left"|"center"|"right", default is "right"), valign
(top|middle|bottom, default is bottom) and append (true|false, default is false)
for adding or replacing existing icons. The image attribute is an object value
with src, width and height for defining the icon to be displayed (default is
mxGraph.warningImage). An empty string for the attribute removes all icons.

Example: JSON.stringify({tooltip: 'Locked', append: true, image:
		{src: IMAGE_PATH + '/locked.png', width: 26, height:26}}

- An optional geometry attribute that contains a JSON mxGeometry object can be used
to replace the current geometry of the refenced cell. In addition to the existing
field names in mxGeometry, dx and dy can be used to define a vector for moving the
shape, and dh and dw can be used to resize the cell.

Example: JSON.stringify({dx: (Math.random() * 100) - 50, dh: (Math.random() * 100) - 50}))

- Additionally a model node may be specified to set the current graph model.

Example: <model><mxGraphModel><root><mxCell id="0"/></mxCell>...</root></mxGraphModel></model>

- A view node may be specified with a scale, dx and dy attribute to change the current
scale and translate.

Example: <view scale="0.5" dx="100" dy="100"/>

- A fit node may be specified with a max-scale property to fit the diagram to the
available viewport with the specified max-scale.