xserver-xephyr - 2:1.20.4-1+deb10u4 main

Xephyr is an X server that can be run inside another X server,
much like Xnest. It is based on the kdrive X server, and as a
result it supports newer extensions than Xnest, including render and
composite.
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More information about X.Org can be found at:

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This package is built from the X.org xserver module.