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We can just close the href attribute and add a target attribute. The problem now is that in the gliffy macro you the image map to make the up part of the window name. I don't see any way of getting that information atm.

Do you think we could use javascript to create the name? Would something like either of these work:

(invoke javascript to create random number between 0-1000000 as target name)
target="&{Math.floor(Math.random()*1000000)};"

OR

(invoke javascript to create a map name similar to how we do it in ConfluencePluginDiagramBiz, assuming we can get the attachment name. We should probably produce an exact match of what we do in ConfluencePluginDiagramBiz if we can)
target="&{ 'GLIFFY_MAP_' + $attachementName.replace(" ","_"); };"

Supposedly you can embed javascript in HTML attributes, tho I've never tried it myself:
http://devedge-temp.mozilla.org/library/manuals/2000/javascript/1.3/guide/embed.html