Generic virtual methods on IL2CPP: how it works?

Documentation [Scripting restrictions](https://docs.unity3d.com/2019.3/Documentation/Manual/ScriptingRestrictions.html) contains restrictions of generic virtual methods on IL2CPP in section **"Generic virtual methods"**. However, the code example given in this section, that should not work on IL2CPP, works fine on Unity 2019.3.0f6 Windows IL2CPP build. I also discovered that our dev team use the generic virtual methods in production without any problems. Please, describe the actual restrictions of the generic virtual methods.