hide/show polylines

Does anyone know of a tutorial showing how to show/hide different
polylines by category on Google maps?
Is the method similar to hiding/showing marker categories as detailed
in Mike Williams tutorial http://econym.org.uk/gmap/categories.htm ?
For example I have created a simple map which shows 2 marker
categories which I can toggle on and off. On the same map I have drawn
2 polylines which I would like to be able to toggle on and off in a
similar fashion.
http://www.peterbertelsen.com/map-test/categories-tr.html

Can this be achieved by declaring a 'category' in the <line> tag in
the xml document, as with the markers, or is there a completely
different method for hiding/showing polylines?

Thanks in advance for any help you can give.

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