Doc: standardise level 5 headings (2730)

 - add subsubsubheading macro for use as level 5
   heading

 - update CG to document its use

 - amend entire Chapter 1 of NR

5 files changed, 42 insertions, 20 deletions

diff --git a/Documentation/common-macros.itexi b/Documentation/common-macros.itexi
index 1fda210772..123c1aa31a 100644
--- a/Documentation/common-macros.itexi
+++ b/Documentation/common-macros.itexi
@@ -77,6 +77,11 @@
 
 @c   ***** Headers *****
 
+@c For use as the Level 5 header
+@macro subsubsubheading {TEXT}
+@subsubheading @i{\TEXT\}
+@end macro
+
 @ifclear snippets-sections
 @macro lydoctitle {TEXT}
 @need 600
diff --git a/Documentation/contributor/doc-work.itexi b/Documentation/contributor/doc-work.itexi
index 8695d340ee..ff6e0f0721 100644
--- a/Documentation/contributor/doc-work.itexi
+++ b/Documentation/contributor/doc-work.itexi
@@ -221,15 +221,33 @@ how to modify the snippet files and SL, see @ref{LSR work}.
 @node Sectioning commands
 @subsection Sectioning commands
 
-Most of the manual operates at the
+The Notation Reference uses section headings at four, occasionally
+five, levels.
+
+@itemize
+
+@item Level 1: @@chapter
+@item Level 2: @@section
+@item Level 3: @@subsection
+@item Level 4: @@unnumberedsubsubsec
+@item Level 5: @@subsubsubheading
+@end itemize
+
+The first three levels are numbered in html, the last two are not.
+Numbered sections correspond to a single html page in the split html
+documents.
+
+The first four levels always have accompanying nodes so they can be
+referenced and are also included in the ToC in html.
+
+Most of the manual is written at level 4 under headings created with
 
 @example
 @@node Foo
-@@subsubsection Foo
+@@unnumberedsubsubsec Foo
 @end example
 
-@noindent
-level.  Sections are created with
+Level 3 subsections are created with
 
 @example
 @@node Foo
@@ -263,11 +281,10 @@ match the node name exactly.
 No commas may be used in the node names.
 
 @item
-If a heading is desired without creating a @code{@@node}, please use
-the following:
+If a heading is desired without creating a @code{@@node}, please use:
 
 @example
-@@subheading Foo
+@@subsubsubheading Foo
 @end example
 
 @item
diff --git a/Documentation/notation/pitches.itely b/Documentation/notation/pitches.itely
index 99e8e0932b..c1b780ad14 100644
--- a/Documentation/notation/pitches.itely
+++ b/Documentation/notation/pitches.itely
@@ -900,7 +900,7 @@ It may also be reversed to produce its @notation{retrograde}, see
 @warning{Any note that does not lie within the given scale will be
 left untransformed.}
 
-@subsubheading Modal transposition
+@subsubsubheading Modal transposition
 
 @cindex modal transposition
 @cindex transposition, modal
@@ -957,7 +957,7 @@ motif = \relative c' { c8 d e f g a b c }
 }
 @end lilypond
 
-@subsubheading Modal inversion
+@subsubsubheading Modal inversion
 
 @cindex modal inversion
 @cindex inversion, modal
diff --git a/Documentation/notation/rhythms.itely b/Documentation/notation/rhythms.itely
index fc3af0d5ef..27c84eae28 100644
--- a/Documentation/notation/rhythms.itely
+++ b/Documentation/notation/rhythms.itely
@@ -1560,7 +1560,7 @@ Explicitly create a @code{Voice} context when starting a piece with
 Polymetric notation is supported explicitly or by manually modifying the
 visible time signature symbol and/or scaling note durations.
 
-@subsubheading Different time signatures with equal-length measures
+@subsubsubheading Different time signatures with equal-length measures
 
 Set a common time signature for each staff, and set the
 @code{timeSignatureFraction} to the desired fraction.  Then use the
@@ -1602,7 +1602,7 @@ affect the autobeaming rules.
 >>
 @end lilypond
 
-@subsubheading Different time signatures with unequal-length measures
+@subsubsubheading Different time signatures with unequal-length measures
 
 Each staff can be given its own independent time signature by
 moving the @code{Timing_translator} and the
@@ -1650,7 +1650,7 @@ moving the @code{Timing_translator} and the
 @cindex compound time signatures
 @cindex time signature, compound
 
-@subsubheading Compound time signatures
+@subsubsubheading Compound time signatures
 
 These are created using the @code{\compoundMeter} function.  The syntax
 for this is:
@@ -2004,7 +2004,7 @@ by
 @end example
 
 
-@subsubheading @i{Beaming based on @code{baseMoment} and @code{beatStructure}}
+@subsubsubheading 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
@@ -2106,7 +2106,7 @@ 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}.
 
-@subsubheading @i{Beaming based on @code{beamExceptions}}
+@subsubsubheading Beaming based on @code{beamExceptions}
 
 Special autobeaming rules (other than ending a beam on a beat)
 are defined in the @code{beamExceptions} property.
@@ -2219,7 +2219,7 @@ r4. a8 a a |
 r4. a8 a a |
 @end lilypond
 
-@subsubheading @i{How automatic beaming works}
+@subsubsubheading How automatic beaming works
 
 When automatic beaming is enabled, the placement of automatic beams
 is determined by the context properties
diff --git a/Documentation/notation/simultaneous.itely b/Documentation/notation/simultaneous.itely
index f633877ac2..458ad6f171 100644
--- a/Documentation/notation/simultaneous.itely
+++ b/Documentation/notation/simultaneous.itely
@@ -384,7 +384,7 @@ multiple staves.
 @funindex \oneVoice
 @funindex oneVoice
 
-@strong{@i{Explicitly instantiating voices}}
+@subsubsubheading Explicitly instantiating voices
 
 The basic structure needed to achieve multiple independent
 voices in a single staff is illustrated in the following example:
@@ -408,7 +408,7 @@ automatically moved to avoid collisions.  The @code{\oneVoice}
 command returns all the voice settings to the neutral default
 directions.
 
-@strong{@i{Temporary polyphonic passages}}
+@subsubsubheading Temporary polyphonic passages
 
 A temporary polyphonic passage can be created with the following
 construct:
@@ -455,7 +455,7 @@ during and after a polyphonic section:
 Here, the @code{\voiceOne} and @code{\voiceTwo} commands are
 required to define the settings of each voice.
 
-@strong{@i{The double backslash construct}}
+@subsubsubheading The double backslash construct
 
 The @code{<< @{...@} \\ @{...@} >>} construct, where the two (or
 more) expressions are separated by double backslashes, behaves
@@ -500,7 +500,7 @@ In all but the simplest works it is advisable to create explicit
 @code{Voice} contexts as explained in @rlearning{Contexts and engravers} and
 @rlearning{Explicitly instantiating voices}.
 
-@strong{@i{Voice order}}
+@subsubsubheading Voice order
 
 When entering multiple voices in the input file, use the following
 order:
@@ -539,7 +539,7 @@ upstems, and the even-numbered voices are given downstems:
 @warning{Lyrics, spanners (such as slurs, ties, hairpins etc.) cannot be
 created @q{across} voices.}
 
-@strong{@i{Identical rhythms}}
+@subsubsubheading Identical rhythms
 
 In the special case that we want to typeset parallel pieces of music
 that have the same rhythm, we can combine them into a single