Base question about indexed VBO arrays

If we only have the ability to use a single index array, how can both Vertices and UVs be indexed by it? Obviously sometimes a vertex would need to have multiple UVs associated with it (e.g. corner of a cube with different texture zones on each face would need three UVs).

You can’t have an index per attribute, only per complete vertex (all vertex attributes), so in these cases you duplicate the vertex position.