Add warning about using \relative with tagged music (3253)

Add warning about using \relative with tagged music (3253)

 - add warning as a known issue
 - remove earlier ignored known issue

[dak, 2013-03-18 18:37:37]

https://codereview.appspot.com/7798045/diff/1/Documentation/notation/input.itely
File Documentation/notation/input.itely (right):

https://codereview.appspot.com/7798045/diff/1/Documentation/notation/input.it...
Documentation/notation/input.itely:2247: @end example
That's \relative without reference pitch...  This particular form would not
actually be used, instead music would be defined as
music =
\relative c' { ...

So I don't think these examples really make things more clear.  There also is no
"correct" and "incorrect" usage.

It is just that it rarely makes sense to apply \relative to music treated with
\keepWithTag/\removeWithTag since then different sequences will be run through
\relative.

However, if you just cut away material at the end of a sequence, or just cut
away articulations, this is not actually a problem.

So the rule more or less is
"Calling \relative on a sequence gained with \keepWithTag/\removeWithTag will
consider only the pitches actually remaining in the sequence, possibly changing
the octave relations."

[Keith, 2013-03-19 08:53:07]

I'm confused by the new text.  I also fail to see the motivation for explaining
this; no-one has reported any confusion with the behavior.

You might just say
"Notice that \keepWithTag can change the pitches used as reference for later
pitches written using relative input mode.  The d below is interpreted as a
fourth below g' or as a third below f'' depending on which tag is kept:
 music = << \tag #'score a \tag #'part f >>
 \relative c'' { c \keepWithTag #'score \music d}
Applying \relative first, then \keepWithTag is the usual method of input, so
that \relative acts on the pitches as-input:
 \keepWithTag #'score \relative c'' { c \music d}
"

https://codereview.appspot.com/7798045/diff/1/Documentation/notation/input.itely
File Documentation/notation/input.itely (right):

https://codereview.appspot.com/7798045/diff/1/Documentation/notation/input.it...
Documentation/notation/input.itely:2236: to notes with pitches expressed in
absolute notation.  If music is
This makes it sound like I cannot do this:

music = \relative c' \new Staff{
  << \tag#'F {f} \tag#'G {g} >>
  c }  % C in relative notation is a fourth above the G
\keepWithTag#'F \music
\keepWithTag#'G \music

https://codereview.appspot.com/7798045/diff/1/Documentation/notation/input.it...
Documentation/notation/input.itely:2239: absolute notation before being filtered
with @code{\keepWithTag} or
I would not think that \relative converted pitches to absolute notation.  The
computer has already read my relative-pitch input notation, and I have no
concept of a 'notation'  at that point.  I suppose \displayLilyMusic does
recreate absolute notation.

[Trevor Daniels, 2013-04-07 21:20:37]

Respond to comments from David and Keith

[Graham Percival, 2013-04-09 07:23:43]

LGTM

[janek, 2013-04-13 14:14:57]

generally LGTM

https://codereview.appspot.com/7798045/diff/5001/Documentation/notation/input...
File Documentation/notation/input.itely (right):

https://codereview.appspot.com/7798045/diff/5001/Documentation/notation/input...
Documentation/notation/input.itely:2246: Calling @code{\relative} on a sequence
obtained by filtering music
I think "expression" or "music expression" would be better than "sequence".

[Trevor Daniels, 2013-04-13 17:38:50]

Repond to Janek's comment

[Trevor Daniels, 2013-04-14 21:41:23]

Pushed to staging as
ee0ef98a35634718033d505deb8a355e05513d6a
Closing ...