Links on Relevant Pages
Everyone who uses the web collects links eventually.
Sometimes these useful links are added to the personal bookmarks (these
are maintained by your browser.)
Providers also collect links.
Links to sites outside of the provider's control often are included
to supplement/support the information being presented.
Sometimes, they are included with the information. Other times they are
all grouped together.
It can take a lot of time to gather valid links, and periodically check
that they still work. Positive feedback via email is welcome. Their work can
save you lots of time and effort.