      command relative to those issued after the barrier. For the purposes of
            this ordering, memory transactions performed by shaders are considered to
            be issued by the rendering command that triggered the execution of the
            shader.  <em class="parameter"><code>barriers</code></em> is a bitfield indicating the set of operations that
            are synchronized with shader stores; the bits used in <em class="parameter"><code>barriers</code></em> are as
            follows:
