Re: strange `break-align-symbols` behaviour

[Werner LEMBERG]

>> there is no key signature at this point, right?
> 
> This is my interpretation: the key signature is removed by
> break-visibility, but the X alignment of a mark is computed before
> that happens.

Thanks.  If your interpretation is correct I consider it as
problematic, since it is not possible to control the alignment of the
`MetronomeMark` grob as intended.  In particular, specifying
`key-signature` in `break-align-symbols` effectively disables the
`non-break-align-symbols` property.

To demonstrate this please have a look at the following example; the
first line is the default as specified in `define-grobs.scm`.


     Werner


======================================================================


\version "2.25.14"

music = {
  \compressEmptyMeasures
  R1*20
  \tempo "Tempo" R1*20
  \tempo "Tempo" \key b\minor R1*20
  \tempo "Tempo" g'1 R1
}


\markup \larger \larger "MetronomeMark"

\markup \vspace #1

\markup "(break-align-symbols . (time-signature))"
\markup "(non-break-align-symbols . (paper-column-interface))"
{
  \override Score.MetronomeMark.break-align-symbols = #'(time-signature)
  \override Score.MetronomeMark.non-break-align-symbols =
    #'(paper-column-interface)
  \music
}

\markup "(break-align-symbols . (key-signature))"
\markup "(non-break-align-symbols . (paper-column-interface))"
{
  \override Score.MetronomeMark.break-align-symbols = #'(key-signature)
  \override Score.MetronomeMark.non-break-align-symbols =
    #'(paper-column-interface)
  \music
}

\markup "(break-align-symbols . (time-signature))"
\markup "(non-break-align-symbols . (note-column-interface 
multi-measure-rest-interface))"
{
  \override Score.MetronomeMark.break-align-symbols = #'(time-signature)
  \override Score.MetronomeMark.non-break-align-symbols =
    #'(note-column-interface multi-measure-rest-interface)
  \music
}

\markup "(break-align-symbols . (key-signature))"
\markup "(non-break-align-symbols . (note-column-interface 
multi-measure-rest-interface))"
{
  \override Score.MetronomeMark.break-align-symbols = #'(key-signature)
  \override Score.MetronomeMark.non-break-align-symbols =
    #'(note-column-interface multi-measure-rest-interface)
  \music
}