Re: Question for a new LilyPond user (parts-only editing)

[David Kastrup]

Flaming Hakama by Elaine <address@hidden> writes:

> On Wed, Dec 6, 2017 at 8:33 AM, David Kastrup <address@hidden> wrote:
>
>> Flaming Hakama by Elaine <address@hidden> writes:
>>
>> > Here is an illustration of using tags for this purpose.
>> >
>> > Note that there are other approaches, even using tags.
>> > This approach uses the \keepWithTag within each \score
>> > to distinguish Part vs Score, PDF vs MIDI, the specific
>> > instrument, and each segment the piece.
>>
>> Really, I'd use
>>
>> \tagGroup SegmentA,SegmentB,SegmentC
>> \tagGroup PDF,MIDI
>> \tagGroup Part,Score
>>
>> with this so that you don't have to list unrelated tags (like
>> SegmentA,SegmentB,SegmentC) whenever you use \keepWithTag for one
>> purpose.
>>
>
> Thanks for the help.  I have to admit, however, I totally don't understand
> this application of \tagGroup.
>
> Maybe \tagGroup has more useful use cases for \removeWithTag?

No.  It's really just for \keepWithTag so that \keepWithTag MIDI does
not throw away things things tagged with \tag SegmentA (and nothing
else).

> Using \keepWithTag already has the effect of excluding any tagged
> content that isn't among the tags specified.

Which is exactly what \tagGroup avoids: is excludes any _related_ tagged
content, but does not consider tags outside of the respective \tagGroup .

> What is gained by specifying a group of tags to ignore, since they are
> already being ignored?

They aren't ignored.

    \tag SegmentA ...

gets removed by \removeWithTag MIDI unless you separate MIDI and
SegmentA into different tag groups.

> In the example in the docs, using tagGroup produces the same result as not
> using it:
>
> http://lilypond.org/doc/v2.19/Documentation/notation/different-editions-from-one-source
>
> \version "2.19.80"
>
> music = \relative {
>   \tag #'violinI { c''4^"violinI" c c c }
>   \tag #'violinII { a2 a }
>   \tag #'viola { e8 e e2. }
>   \tag #'cello { d'2 d4 d }
>   R1^"untagged"
> }
>
> \new Voice {
>   \mark "No tagGroup"
>   \keepWithTag #'violinI
>   \music
> }
>
> \new Voice {
>   \mark "With tagGroup"
>   \tagGroup #'(violinI violinII viola cello)
>   \keepWithTag #'violinI
>   \music
> }
>
>
> So, what is \tagGroup really doing in this case?

Ouch.  Nothing.  The example is junk because it only contains a single
specified tag group (and essentially all tags not in a specified tag
group are implicitly in a single tag group anyway).

The original documentation I wrote contained no examples.  This was
added as

commit c5847c9329abba798fb15bb336c7247ab149660b
Author: James Lowe <address@hidden>
Date:   Thu Feb 18 10:43:09 2016 +0000

    Doc: NR - input.itely: Various improvements
    
    Issue 4677
    
    A variety of nitpicks and
    improvements reported by
    Federico Bruni
    
    Updated information and
    included a new @lilypond
    example for \KeepWithTag.
    
    Some spelling corrections
    and some simple rewording
    of a few paragraphs for
    clarity (deleted repeated
    words, removed personal
    pronouns etc.).
    
    Moved a comment (@c) outside
    of an @example so as to not
    cause confusion to readers.

and obviously I shirked properly reviewing it.  Basically \tagGroup only
makes sense if you at least have two different tag groups (one may be
the implied default one): only then does the behavior start to differ.
Of course it also makes sense to use in style files using tags
internally: putting the internally used tags in a tag group means that
they won't interfere with tags the user uses himself in his source code.

> If you explain it to me, I can try to come up with a better example
> for the docs.

It's for the case where you are dealing with orthogonal tags:
\keepWithTag violinI should not throw away a sequence marked only
\tag MIDI because MIDI and violinI have nothing to do with one another.

-- 
David Kastrup