Gwlp_userdata

[Igor Vartanov]

So userdata means what is typed in the window for example or the coordinates of the window?

Userdata here means any data that programmer wants to attach to this tab. This may be a pointer to byte array, or string object, or predefined user structure instance, or user class object, whatever you want this to be. You may think of it like a locker where you put your valuable things (data) and leave those there until you need to reach to.