harmonicByRatio usage... plus harmonicsOn and TabStaff

[Federico Bruni]

I have two questions about harmonics.
First one is about harmonicByRatio.  I've seen in the command index that
it is undocumented (like harmonicByFret).
There's an explanation here:
http://lilypond-s-support-for-tablatures.3383434.n2.nabble.com/harmonics-in-tablature-td5518526.html
 

But it's a bit difficult for me right now.
Can you help me?

Also, I've noticed that \harmonicsOn works only in Staff and not in
TabStaff.  There's a reason for this behavior or it's a bug?

Finally, after calling \harmonicByRatio the following harmonics are
raised by one octave.  Again, a bug or I'm missing something?

You can see everything in the attached example.

Thanks in advance,
Federico

harmonicByRatio.ly
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