Any significant structural diversion from boilerplate.html in a specific article may result in errors from GNUN. Any untested intrusive updates to the server templates (such as changing the entire look & feel of the site) will probably break GNUN build process. Of course, this does not mean that no changes should happen—only that they must be applied in a sandbox first, to ensure a smooth transition.
gnun-validate-html is useful for webmasters who
want to verify if their (potentially intrusive) changes result in a
valid markup. Before committing your changes, you can check whether
the file is valid by running
gnun-validate-html --root . philosophy/not-ipr.html
See gnun-validate-html, for more information.