Doc: Clarify automatic beam setting (2701) (issue 6452072)

[tdanielsmusic]

Reviewers: ,

Message:
For Graham, really:


http://codereview.appspot.com/6452072/diff/1/Documentation/notation/rhythms.itely
File Documentation/notation/rhythms.itely (right):

http://codereview.appspot.com/6452072/diff/1/Documentation/notation/rhythms.itely#newcode2007
Documentation/notation/rhythms.itely:2007: @address@hidden based on
@code{baseMoment} and @code{beatStructure}}}
I don't like this either, but it was already used elsewhere in this
section.  We already have unnumberedsubsubsec, so can't use that.

Description:
Doc: Clarify automatic beam setting (2701)

Explain at the beginning the precedence of the
rules, and include an example to show how to
disable beamExceptions.

Please review this at http://codereview.appspot.com/6452072/

Affected files:
  M Documentation/notation/rhythms.itely


Index: Documentation/notation/rhythms.itely
diff --git a/Documentation/notation/rhythms.itely  
b/Documentation/notation/rhythms.itely
index  
ed9424c45550e97fe87711672944f980132d6615..79859641291d21ceb7ba37c83e86465647896b9b  
100644
--- a/Documentation/notation/rhythms.itely
+++ b/Documentation/notation/rhythms.itely
@@ -1984,6 +1984,28 @@ new beam starts.
 @funindex \set
 @funindex set

+When automatic beaming is enabled, the placement of automatic beams
+is determined by three context properties:
address@hidden, @code{beatStructure}, and @code{beamExceptions}.
+If a @code{beamExceptions} rule is defined for the time signature in
+force, that rule is used to determine the beam placement.  If no
address@hidden rule is defined for the time signature in force,
+the beam placement is determined by the settings of @code{baseMoment}
+and @code{beatStructure}.
+
+By default, @code{beamExceptions} rules are defined for most common
+time signatures, so the @code{beamException} rules must be disabled
+if automatic beaming is to be based on @code{baseMoment} and
address@hidden  The @code{beamExceptions} rules are disabled
+by
+
address@hidden
+\set Timing.beamExceptions = #'()
address@hidden example
+
+
address@hidden@strong{Beaming based on @code{baseMoment} and 
@code{beatStructure}}}
+
 In most instances, automatic beams will end at the end of a beat.
 The ending points for beats are determined by the context properties
 @code{baseMoment} and @code{beatStructure}.  @code{beatStructure}
@@ -2001,6 +2023,25 @@ c16^"(2+3)" c c c c |
 c16^"(3+2)" c c c c |
 @end lilypond

+If a common time signature is being used, @code{beamExceptions}
address@hidden be disabled to enable @code{beatStructure} to work.
+The @code{\set Timing.beamExceptions = #'()} command can always
+be included if beaming is being determined by @code{beatStructure}.
+
address@hidden,relative=2,verbatim]
+\time 4/4
+a8^"default" a a a a a a a
+
+\set Timing.baseMoment = #(ly:make-moment 1 4)
+\set Timing.beatStructure = #'(1 1 1 1)
+a8^"no change" a a a a a a a
+
+\set Timing.beamExceptions = #'()
+\set Timing.baseMoment = #(ly:make-moment 1 4)
+\set Timing.beatStructure = #'(1 1 1 1)
+a8^"changed" a a a a a a a
address@hidden lilypond
+
 Beam setting changes can be limited to specific contexts.  If no
 setting is included in a lower-level context, the setting of the
 enclosing context will apply.
@@ -2065,6 +2106,8 @@ By default @code{baseMoment} is set to one over the  
denominator of
 the time signature. Any exceptions to this default can be found in
 @file{scm/time-signature-settings.scm}.

address@hidden@strong{Beaming based on @code{beamExceptions}}}
+
 Special autobeaming rules (other than ending a beam on a beat)
 are defined in the @code{beamExceptions} property.