http://www.gentoo.org/proj/en/qa/asneeded.xml It's on by default so we should document it as such and support it.
Done, thanks.
Reopening as the document to day states as-needed is "not considered safe for production use and not supported in any way by Gentoo", which should probably be dropped, per comment #0. (It's the warning block right under "How to use as-needed".)
Created attachment 299251 [details, diff] asneeded.xml.patch Patch to remove the warning box as noted in comment #2.
Thank you for filing this bug, done in https://wiki.gentoo.org/index.php?title=Project%3AQuality_Assurance%2FAs-needed&diff=139129&oldid=79203