I'm sorry for not making it more clear, but that was just an example of something left unspecified by the X11 core protocol but instead defined in a standard convention.

An example that matters for window managers would be complex window reparenting policies or input grabs, but that's a little less descriptive of the core concept I was trying to get across.

We may not always have Paris, but we will always have XRotateBuffers.

https://tronche.com/gui/x/xlib/utilities/XRotateBuffers.html