A url item stored as javascript://%0aalert(1)%0a//x passed Url::to and
reached <loc>, which sitemap.xsl renders as a link on the site origin.
- The definitions form refuses, per row, a url that is not a path or an
http(s) URL (classes.AllowedItemURL) and a urlPattern that is not a
path (signpost.ValidItemPattern), keyed data.<i>.url / .urlPattern.
- Generator.addItem drops a loc or alternate that is not http(s).
- sitemap:import-winter drops such url items and clears such patterns
with a report line; sitemap:import refuses such an entry.