Re: Disabling self-alignment-X

>> It’s so helpful for illustrating reference point, horizontal
>> extent, and vertical extent
> 
> I have a few questions/clarifications:
> 
> 1. Is the vertical extent (-10, 29) and the horizontal extent (-9,
> 26), or are they equal to some other values [possibly incorporating
> some offset]?

I guess you've missed the sentence right before the image:

  In the image below, the point with zero coordinates is the reference
  point; the horizontal extent is #'(-9 . 26), the vertical one is
  #'(-10 . 29).

> 2. Why are there portions of the glyph that extend beyond the h/v
>    extent?

See

  https://lilypond.org/doc/v2.27/Documentation/extending/lilypond_0027s-box-model

I will add a link to this section.

> 3. Are those “extra-extent” portions caught in/by the skylines?
>    Or padding?

In skylines, they are caught.  However, by default they are not
handled while computing a score's global bounding box.

> Or something else?

You need special code to get them included in the global bounding box
– this is only relevant if you are going to crop the output later on,
otherwise the issue is not important.  See the markup command
`\with-true-dimensions` in

  https://lilypond.org/doc/v2.27/Documentation/notation/text-markup-commands#other-markup-commands

which you can use as

```
\markup \with-true-dimensions \score {
  ...
}
```


    Werner