Unique to the Cube Engine games, cooperative editing lets you build and modify maps with others seamlessly. This mode allows you to just switch to the edit mode online, just like as if you were editing locally. Some functions however are not available in coopedit, namely the undo function, along with some convenient commands like gamespeed and heightmapping.
Saving and Resuming Coopedit Sessions
Lighting and saving, is done client-side, so while still completely functional, it requires cooperation to keep everyone in the server up to date. This means if you do a calclight, everyone else will still be on fullbright or the previous calclight. Saving will just save a local copy of the current map to the hard drive, think of it as "dumping" the map off the server, rather than saving. So if you're with some friends, urge them all to save the map periodically so you don't lose your work.
When resuming a coopedit session, simply use the commands sendmap and getmap to send and receive the map through the server, respectively. Note that with this method, CFG files are not sent, meaning if you've got a custom texture list in the map's CFG, everyone else will see another random set of textures instead. If you're going to coopedit with a custom config, you'll need to send the map config by other means to your friends editing with you. People who join won't be able to see the map unless they getmap, so you should probably set the server to private (using mastermode).
Coopedit is just that -- you can add to other's work or remove it. It is poor form to delete others' work without their consent, just like it wasn't nice to destroy the other kid's castle in the sandbox. Editors try to not work next to each other to avoid interference.
When choosing a server to coopedit on with your friends, use common sense. Server hosts despise editors who join a 32 player server and set it to private. There are many specialized coopedit servers which might have client limits of six or less, which is more than you'd want in a typical coopedit anyway -- four or five players is generally more than enough. As a general guide, servers with eight player slots or above shouldn't be used for coopedit, you could be stopping a group of players from having a game of capture, which they can't do on the smaller four to six player slot servers.
Learn to control your temper. If a newbie joins and starts messing with your map, don't lose it. Explain calmly and concisely why you don't want them to do whatever they are doing, and try to give them a few pointers. If you don't want outsiders to join, set the server to private (mastermode 3).
Coopediting can speed up redundant, repetitive, or redundant processes -- especially useful for large and complicated maps, like smoothing lots of curves or building long stairways. Other editors can fix errors that you didn't notice -- possibly with methods you didn't know about. It's important in coopedit to share editing techniques, so that even newbies can help you out. Think of editing Sauerbraten maps as writing wiki articles: anyone can contribute, and even if suffering some damage (inflicted deliberately or not) it can be reverted back to a normal state.