 index of
            the active interface block containing an active variable is written to
            <em class="parameter"><code>params</code></em>.  If the variable is not the member of an interface block, the
            value -1 is written to <em class="parameter"><code>params</code></em>.
        </p>
        <p>
            For the property <code class="constant">GL_OFFSET</code>, a single integer identifying the offset of an
            active variable is written to <em class="parameter"><code>par