[1] .: Half-Life Protocol -- the official website :. <http://www.stivan.dk/hlprotocol/#web> (名無しさん)

[2]

In v3.6 another URL Protocol has been added (steam). This makes it possible to force users to upgrade their client for Steam-support. The new protocol goes something like this:

<a href="steam://[ip]:[port]> Click and FRAG! </a>

Of course, both protocols (halflife:// & steam://) will work just the same, only difference being that steam:// forces the user to upgrade from previous versions.

[3] Steam browser protocol - Valve Developer Community (2015-05-11 05:02:38 +09:00 版) <https://developer.valvesoftware.com/wiki/Steam_browser_protocol>