The Templates Window (see screenshot) is available in XSLT debugging sessions only; it is not available in XQuery debugging sessions.
The Templates Window displays the various templates used in the XSLT stylesheet, including built-in templates and named templates. Matched templates are listed by the nodes they match. Named templates are listed by their name. For both types of template, the mode, priority, and location of the template are displayed.
In the screenshot above, there are three matched templates in the XSLT stylesheet: a template which matches the document node /, and templates that match the n1:italic and n1:bold nodes. All the other templates are built-in templates (indicated with an entry to that effect in the Location field).
Clicking an entry in this window, causes the template to be highlighted in the XSLT document window. If you click a built-in template, the template is highlighted in a separate window that displays all the built-in templates.