Building sec-policy/selinux-base with USE flag +doc installs html documentation in /usr/share/doc/selinux-base-<version>/<selinuxtype>/html/
This is currently being labeled as usr_t but should be labelled as httpd_sys_content_t.
To resolve being able to read it through Nginx I ran `semanage fcontext -a -t httpd_sys_content_t "/usr/share/doc/selinux-base(-.*)?/(mcs|targeted|strict|mls)/html(/.*)?"`.
I think this should be added to the base policy as well as html is usually read through a http server.
Looks like the refpolicy already contains this, although at "/usr/share/selinux-policy[^/]*/html(/.*)?".
(running on 2.20180701-r2)