Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally

Packages describing “doc” as local USE flag

Package “doc” Flag Description
dev-libs/libnl Install development documentation
dev-libs/libp11 Generate and install API documentation for the package.
media-sound/pulseaudio Build the doxygen-described API documentation.
dev-libs/boost Install the full API documentation documentation. This takes over 200MB of extra disk space.
x11-wm/i3 Build and install the HTML documentation and regenerate the man pages
games-engines/solarus Install doxygen developer documentation.
dev-util/perf Build documentation and man pages. With this USE flag disabled, the --help parameter for perf and its sub-tools will not be available. This is optional because it depends on a few documentation handling tools that are not always welcome on user systems.
app-crypt/mit-krb5 Creates and installs the API and implementation documentation. This is only useful if you want to develop software which depends on kerberos
app-i18n/pyzy Generate API documentation
mail-client/alot Install user manual and API documentation
media-gfx/blender Build C and Python API documentation directly from the source code.
dev-libs/libunibreak Install html API documentation.
media-libs/webvfx Install doxygen developer documentation
net-firewall/nftables Create man pages for the package (requires app-text/asciidoc)
app-emulation/open-vm-tools Generate API documentation
net-analyzer/cacti install html documentation
net-mail/notmuch Install API documentation
net-libs/c-client Install RFCs related to IMAP
app-misc/muttprint Builds documentation
app-portage/eix Create description of the eix cache file additionally in html format
net-analyzer/munin Build and install a local copy of the HTML documentation for the whole software. This requires dev-python/sphinx to process the documentation sources.
dev-lisp/cmucl Installs package documentation
games-rpg/dreamweb High-resolution scans of the written material in the original UK game box
media-gfx/gnofract4d Install user manual
dev-python/icalendar Generate examples and other extra documentation
x11-misc/alock Build and install manpage with app-text/asciidoc.
x11-misc/picom Build documentation and man pages (requires app-text/asciidoc)
sys-devel/llvm Build and install the HTML documentation and regenerate the man pages
sys-apps/pacman Install extended documentation using app-doc/doxygen. (Man pages are included by default.)
sys-libs/ldb Builds documentation
dev-lisp/clx Builds documentation
x11-wm/stumpwm Include documentation

All packages providing a “doc” USE flag (3403)