te</span><span class="special">&lt;</span><span class="keyword">typename</span> Expr<span class="special">&gt;</span> <span class="emphasis"><em><span class="identifier">unspecified</span></em></span> <a name="idp53393520-bb"></a><span class="keyword">operator</span><span class="special">[</span><span class="special">]</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Expr</span> <span class="special">&amp;</span> expr<span class="special">)</span> <span class="