Manual:GMCP Extensions
Automatic package installation
Mudlet supports automatic download and setup of Mudlet packages should the MUD server offer it. These packages could consist of graphical additions to your game or anything else you'd like your players to have loaded on their Mudlet profiles by default. This setup is automatic and carefree on part of the user, and handles package updates in a transparent manner as well.
setup
After GMCP is negotiated, the server should send a string in the format of:
Client.GUI <package version>\n<url>
And Mudlet will make it happen. If the user does not have a package, it will be downloaded and installed from the <url>, and if they do, but of an older version - it'll be upgraded. If they're already on the latest, nothing happens.
demonstration
Connect to godwars2.org on port 3000. Mudlet will download the GW2 interface and set it up automatically (via ATCP, but it's the same).
Sample string sent by GodWars 2:
"Client.GUI 1\nhttp://www.godwars2.org/download/mudlet/GW2_GUI.mpackage"