libx11-dev - 2:1.8.7-1+b1 main

This package provides a client interface to the X Window System, otherwise
known as 'Xlib'. It provides a complete API for the basic functions of the
window system.
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This package contains the development headers for the library found in
libx11-6. Non-developers likely have little use for this package.
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More information about X.Org can be found at:

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This module can be found at
https://gitlab.freedesktop.org/xorg/lib/libX11