What qualifies as the required shelter?

A shelter qualifies if it keeps out rain and wind and is free standing. This could be as simple as a small tarp or large piece of plastic pitched over trekking poles. BUT please keep in mind that an injury as simple as a broken ankle can be life threatening in the extreme cold. The idea is that if you are injured and need to stop, you can call for help and then change into dry clothes, get in your SHELTER, and even start a fire until help arrives.