DocBook/drm: Better flow with `, and then'

      <para>

	Perhaps the most important GEM function is providing a command

	execution interface to clients.  Client programs construct command

	buffers containing references to previously allocated memory objects

	and submit them to GEM.  At that point, GEM takes care to bind

	buffers containing references to previously allocated memory objects,

	and then submit them to GEM.  At that point, GEM takes care to bind

	all the objects into the GTT, execute the buffer, and provide

	necessary synchronization between clients accessing the same buffers.

	This often involves evicting some objects from the GTT and re-binding