The definition of Web unit may not work for SVG.
We have modified the term "Web unit" to be "Web page" and have updated the definition, http://www.w3.org/TR/2007/WD-WCAG20-20070517/#webpagedef .
Web page
a resource that is referenced by a URI and is not embedded in another resource, plus any other resources that are used in the rendering or intended to be rendered together with it
Note: Although any "other resources" would be rendered together with the primary resource, they would not necessarily be rendered simultaneously with each other.
Example 1: When you enter http://shopping.example.com/ in your browser you enter a movie-like interactive shopping environment where you visually move about a store dragging products off of the shelves around you into a visual shopping cart in front of you. Clicking on a product causes it to be demonstrated with a specification sheet floating alongside.
Example 2: A Web resource including all embedded images and media.
Example 3: A Web mail program built using Asynchronous JavaScript and XML (AJAX). The program lives entirely at http://mail.example.com, but includes an inbox, a contacts area and a calendar. Links or buttons are provided that cause the the inbox, contacts, or calendar to display, but do not change the URL of the page as a whole.
Example 4: A customizable portal site, where users can choose content to display from a set of different content modules.