In the example URL, which you get by selecting a namespace from the standard Special:Contributions page for a user, the link to feed URL is wrong both in sidebar and in the metadata (used e.g. by the browser feed icon now moved to extensions like https://addons.mozilla.org/en-us/firefox/addon/rss-icon/ ):
<link rel="alternate" type="application/atom+xml" title="Feed Atom per "Special:Contributions"" href="/w/api.php?action=feedcontributions&user=Nemo+bis&feedformat=atom" />
<li id="feedlinks"><a href="/w/api.php?action=feedcontributions&user=Nemo+bis&feedformat=atom" id="feed-atom" rel="alternate" type="application/atom+xml" class="feedlink" title="Feed Atom per questa pagina">Atom</a></li>
action=feedcontributions is documented only on https://meta.wikimedia.org/w/api.php : namespace, year, month, tagfilter, deletedonly, toponly are available but not linked.
Version: 1.22.0
Severity: normal
URL: https://meta.wikimedia.org/w/index.php?limit=50&tagfilter=&title=Special%3AContributions&contribs=user&target=Nemo+bis&namespace=8&tagfilter=&year=2013&month=-1