Update about beam collision in the docs. (issue4431058)

[mtsolo]

Reviewers: ,

Message:
I did my best to figure out a way to handle automatic beams before staff
changes, but the best I could come up with was a system where a beam was
created every time the automatic beam engraver considered starting a
beam, which leads to a lot of dead grobs that could potentially slow
lilypond wayyyy down.

So, I went with Graham's suggestions to kill beam collision avoidance
for cross-staffs and deal with the
right-before-cross-staff-automatic-beam problem with this doc patch.

Description:
Update about beam collision in the docs.

Please review this at http://codereview.appspot.com/4431058/

Affected files:
  M Documentation/changes.tely
  M Documentation/notation/keyboards.itely


Index: Documentation/changes.tely
diff --git a/Documentation/changes.tely b/Documentation/changes.tely
index  
0c468b14beec2e2583c47026cde5454db194d3a8..8c6563cfb38001f1e5fbd17f5f1a5f808a8eadda  
100644
--- a/Documentation/changes.tely
+++ b/Documentation/changes.tely
@@ -62,6 +62,13 @@ which scares away people.
 @end ignore

 @item
+Lilypond now helps beams avoid collisions with other grobs!  This feature
+works completely with manual beams.  It also works for all automatic beams
+that do not end right before a change in staff.  For this special case,  
please
+use manual beams.  Note that beam collision avoidance does not kick in for
+cross-staff beams.
+
address@hidden
 The Articulate script by Peter Chubb, which is GPLv3 licensed, is now
 a part of the distribution.  It allows easy generation of improved
 MIDI files that perform non-legato by default, legato slurs, staccato,
Index: Documentation/notation/keyboards.itely
diff --git a/Documentation/notation/keyboards.itely  
b/Documentation/notation/keyboards.itely
index  
11acf92a1270fe1fcacb5fd9e26c800b170f8c07..a7f12cd1a96f55520ee2a23bf7241179e64ee74e  
100644
--- a/Documentation/notation/keyboards.itely
+++ b/Documentation/notation/keyboards.itely
@@ -229,6 +229,11 @@ affected by a cross-staff spanner.
 The resulting collisions must be resolved manually, where necessary,
 using the methods in @rlearning{Fixing overlapping notation}.

address@hidden
+Beam collision avoidance does not work for cross-staff beams, nor does
+it work for automatic beams that end right before a change in staff.
+To make the latter work, use manual beaming.
+
 @seealso
 Learning Manual:
 @rlearning{Fixing overlapping notation}.