The Esri-specific XSLT_TEMPLATE parameter can be used to customize WMS -GetFeatureInfo responses since ArcGIS Server 10. This method is preferable to the alternative of modifying the XSLT template on the server according to the documentation (http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//005300000228000000). However, ArcGIS Desktop does not provide a way to specify the XSLT_TEMPLATE paramter when connecting to a WMS. Therefore, the XSLT_TEMPLATE parameter is mainly useful for custom WMS clients. Consider the following use case: A certain text field contains a URL. The attribute table of the WMS should display this field as an HTML link. This could be achieved by means of the XSLT_TEMPLATE parameter as demonstrated with a link to wikipedia in the documentation (http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//005300000228000000). Unfortunately, the XSLT_TEMPLATE parameter cannot be used in ArcMap or ArcCatalog and for that reason, the URL will not display as a link.