Feature request: independent upper and lower staff markings

[Heikki Johannes Junes]

The analysis brackets -\startGroup ... -\stopGroup can nowadays be
nested. However, sometimes you want to show two things which happen at
the same time and need analysis brackets which are not nested. The other
analysis bracket could be above the staff and the other below the staff:

\score {
  \notes \relative c' {
    e8^\startGroup d b_\startGroup c^\stopGroup a b c_\stopGroup
  }
  \header {
    piece = "Two nesting Cambiatas in Palestrina style."
  }
}

If the direction is specified in the post-fixed syntax, it should be
specified both in the beginning and ending part of the syntax. That would
make it possible to double the number of markings belonging to a staff
and more analysis could be shown in a staff.

So, why not double the number of markings, by matching, for example, ^(
with ^) and _( with _), while for -( -) there would be attached a flag
which attaches it to the "upper" or "lower" marking group. This could be a
major enhancement to be developed in LilyPond 1.9 series, if there is
not an easy workaround.

Greetings,

  Heikki Junes