The XCenter does not run on the same thread as most other WPS windows -- which is normally thread 1 in the WPS process. Instead, when an XCenter is opened, a new thread is created. This way we can control the priority of the XCenter display independently from the rest of the WPS.
Note that the XCenter will always use the "regular" priority class to avoid system hangs and side effects with other software. Only within that class you may alter the priority delta between zero and 31.
Per default, the XCenter runs with a priority delta of zero, which is the standard priority delta (and the same as all other WPS windows). However, you can raise that delta up to 31 (which is the maximum priority delta in OS/2) to give the XCenter precendence over other tasks in the system. Among other things, this might make animations run more smoothly.
See "Processes and threads" for more information
about thread priorities.