 attribute index
    to be bound to this variable is specified by
    <em class="parameter"><code>index</code></em>. When
    <em class="parameter"><code>program</code></em> is made part of current state,
    values provided via the generic vertex attribute
    <em class="parameter"><code>index</code></em> will modify the value of the
    user-defined attribute variable specified by
    <em class="parameter"><code>name</code></em>.</p><p>If <em class="parameter"><code>name</code></em> refers to a matrix
   