The effort proceeded in parallel with the Web Mapping Testbed initiative. GML has yet to be adopted as a specification because some of the more advanced parts are not fully mature. Galdos Systems, Inc. is one of GML's advocates. And, with work being done to ensure XML can be run on many platforms, like PDAs, XML opens many doors. As GML grows, more tags will be added.
Vendors are able to add to it for their own use, as many have already begun to do.
The other half of the story for XML in GIS involves the display of XML graphics. Since XML is about text, to show vector graphics, like those typical of GIS, we need something more. Several groups have been working on XML based solutions for vector graphics. Perhaps the most talked about was VML, Vector Markup Language. Office 2000 will create graphics in VML from Word and Powerpoint.