hi, which characteristics must a playmat file have to be loaded in a plugin and is it possible to include it a plugin to make it available automaticcaly when the plugin is installed/loaded?
Yes there is a way. Do you want it to load with a plugin you are making?
exactly
You can have the playmat image download to images/backgrounds/ so it can be used in any game.
The problem with making a playmat automatically selected when you install a plugin is that it has the potential to override a person's ability to choose another. You could include a pluginpreferences.txt file with your plugin download, but it is very important that you make its checksum 0. (Or was it -1... I forget which off hand.) What that will do is not overwrite a pluginpreferences.txt if they already have one. If you didn't do that, you would be constantly overwriting their preferences, which would be annoying. That's why it is usually a bad idea to include pluginpreferences.txt in updatelist.txt.