Which <vtml_partofsp> function to use?

I'm adding some audio under speech management.

When I try <vtml_partofsp part="noun">BOMs </vtml_partofsp>, the audio says it in one word but when I try to add  BOM, it spells it out as BOM vs calling it out as BOM.

Does anyone know which syntax under <vtml_partofsp part> that I should use? I tried the following attributes and not getting much success for the audio calling it BOM (one word)  as listed below

<vtml_partofsp part="unknown" | "noun" | "verb" | "modifier" | "function" | "interjection">

Regards

AJ