Wayland protocol clarification questions

[Tarek Sander]

Hello,

I want to write a Wayland compositor and while reading the protocol 
specification, I noticed some things that aren't clear to me:

- How does the input and opaque region of a surface behave on a resize? 
Do the additional pixels get automatically added for the input region?

- Is it valid for the wp_presentation_feedback::kind bitfield to contain 
no flag at all?

- What exactly is the anchor rectangle of an xdg_positioner?

Thanks,

Tarek