app-text/docbook-sgml-utils-0.6.14 depends on virtual/textbrowser and virtual/textbrowser is not defined.
Created attachment 92107 [details, diff] Patch to add virtual/textbrowser I patched /usr/portage/profiles/default-linux/virtuals for testing
According to the ChangeLog, the docbook-sgml-utils ebuild doesn't have the virtual/textbrowser dependency since April 5.