Update: changed for NetBeans 6.5
I use Cocoon for my work related projects and I want to edit the sitemap and configuration files with XML support in NetBeans. Fortunately this is very easy. We need to go to Tools | Options | Advanced Options. In the Advanced Options dialog window we go to IDE Configuration | System | Object Types | XML Objects. On the right we now have a property called Extension and MIME Types. We click on the ... button and now we can add more extensions. For example we add
xconf for Cocoon related files. We now close the dialog windows and when we open a
sitemap.xmap file in NetBeans we get full XML support.