XSLT - input document processing

First, the processor selects the document root (not the root element) - corresponding to the XPath expression /

Then the processor finds a matching template (explicit or implicit - see eg. XSLT/XPath Quick Reference), where the match attribute as an XPath predicate returns true in the context of the current node ("matches" the current node).

if there are more matching templates and they cannot be distinguished/ordered by priority - an error is indicated.

if there is just one such template, it is applied, ie. its body is translated into the result tree fragment.