API:KSPField

KSPField is a C# annotation that may be applied to member variables of API:Parts, API:PartModules, etc to make their state persistent.

e.g.

class MyBlingModule : PartModule
{
    [KSPField()]
    protected double blingBrightness = 1000.0;

    //...
}

adds a field that is exposed to ModuleManager, saved and restored by KSP on load and unload, etc.