Semantics of <expan>, <ex> and <am> tags in TEI

Question

For abbreviations, the TEI documentation §11.3.1.2 recommends using either <abbr> with <am> or <expan> with <ex>. But what happens with a case like the German clipping bzw. (= beziehungsweise). Letters "b", "z" and "w" belong both to the abbreviation and the expansion, but the period belongs only to the abbreviation. I would write it as

<expan>b<ex>e</ex>z<ex>iehungs</ex>w<ex>eise</ex><am>.</am></expand>

so that "b", "z" and "w" are outside the <ex> and <am> tags and the period is inside the <am> tag.

Is that correct?

It is not what TEI recommends (in no example do I see an <am> inside an <expan>) but I see no other way to have the three cases:

1. characters only in abbreviation (which I put inside <am>),
2. characters only in expansion (which I put inside <ex>), and
3. characters both in abbreviation and in expansion (which I put outside both <ex>and <am>).