In addition, this example won't work well with hundreds or thousands of records without enhancements. XSLT presents XML content formatted for the browser or other medium. You can think of an XSLT style sheet as a template for displaying XML data, similar to a template used in a mail merge. A style sheet describes the XML data's format and transforms the data into that format, such as a mail merge, where a template document is populated with mail merge data. You can use templates to refer to the data you want to display.
Templates attach to particular nodes of the XML document.
In this case, you attach to the Addresses node that contains all record-level nodes. Once you obtain this reference to the Address node with the select attribute, you can start navigating through the source document from this context. The HTML in your style sheet acts as a template, in which you use XSLT to describe the data to display within the template. XSLT style sheets are XML documents, so they must conform to the XML document standards. Data islands are XML data inside HTML pages.