Valence electrons

For the paragraph on valence electrons, what does it mean when it says that the valence electrons are those in the d subshell of the "next to outermost" energy shell or the "f subshell of the energy shell 2 levels below the outermost shell?"  How do we know what the outermost shell is and what does it mean "next to outermost" or "2 levels below the outermost shell?"
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I think this paragraph is confusingly written in the book.  Let me put it this way:
If you are in the s block, the valence electrons are the highest s electrons.
If you are in the p block, the valence electrons are the highest s and p electrons only.
If you are in the d block, the valence electrons are the highest s and d electrons only.
If you are in the f block, the valence electrons are the highest s and f electrons only.

A few examples:
Mg = [Ne] 3s².  Valence electrons are thus 3s².

Sb = [Kr] 5s² 4d¹⁰ 5p³.  Valence electrons are thus 5s² 5p³.

Os = [Xe] 6s² 4f¹⁴ 5d⁶.  Valence electrons are thus 6s² 5d⁶.

Fm = [Rn] 7s² 5f¹².  Valence electrons are thus 7s² 5f¹².