ref="reference.html#parameterspec"><span class="concept">ParameterSpec</span></a>.  As introduced described in the section on <a class="reference internal" href="#class-template-signatures">Class
Template Signatures</a>, a <span class="concept">ParameterSpec</span> describes the positional
order of parameters and any associated type requirements.  Just as
we can build an <span class="concept">ArgumentPack</span> <em>type</em> with its nested <tt class="docutils literal">::bind&lt; …
&gt;</tt> template, we