x11-libs/libXcomposite-0.4.1 has a dependency on xmlto, but as far as I can tell, the package doesn't actually need xmlto in order to build (simply removing xmlto from the DEPEND list allowed it to build with no problems), so the dependency should be removed. Patch to follow, for what it's worth.
Created attachment 206859 [details, diff] Remove app-text/xmlto from libXcomposite DEPEND list
Sorry, that was probably not worded as politely as it should have been. Was there a particular reason for adding the xmlto dependency in libXcomposite-0.4.1?
It was added at some point to the x11 overlay and that's where portage ebuilds come from. I've put it behind a doc USE flag instead, since some users might still be interested by the man pages. Thanks