  By the example of sp^3-bonded semiconductors, we illustrate what
3rd-generation muffin-tin orbitals (MTOs) are. We demonstrate that they can be
downfolded to smaller and smaller basis sets: sp^3d^10,sp^3, and bond orbitals.
For isolated bands, it is possible to generate Wannier functions a priori. Also
for bands, which overlap other bands, Wannier-like MTOs can be generated a
priori. Hence, MTOs have a unique capability for providing chemical
understanding.
