lass="parameter"><code>index+2</code></em>,
    and <em class="parameter"><code>index+3</code></em> for a matrix of type
    <code class="function">mat4</code>.</p><p>This command makes it possible for vertex shaders to use
    descriptive names for attribute variables rather than generic
    variables that are numbered from 0 to
    <code class="constant">GL_MAX_VERTEX_ATTRIBS</code> -1. The values sent
    to each generic attribute index are part of current state.
    If a different program object is made