Contexts are arranged hierarchically:
@menu
+* Output definitions - blueprints for contexts::
* Score - the master of all contexts::
* Top-level contexts - staff containers::
* Intermediate-level contexts - staves::
* Bottom-level contexts - voices::
@end menu
+@node Output definitions - blueprints for contexts
+@unnumberedsubsubsec Output definitions - blueprints for contexts
+
+This section explains the relevance of output definitions when
+working with contexts. Examples for actual output definitions are
+given later (see @ref{Changing all contexts of the same type}).
+
+@cindex output definitions
+@funindex \layout
+While music written in a file may refer to context types and
+names, contexts are created only when the music is actually being
+interpreted. LilyPond interprets music under control of an
+@q{output definition} and may do so for several different output
+definitions, resulting in different output. The output definition
+relevant for printing music is specified using @code{\layout}.
+
+@funindex \midi
+A much simpler output definition used for producing Midi output is
+specified using @code{\midi}. Several other output definitions
+are used by LilyPond internally, like when using the part combiner
+(@ref{Automatic part combining}) or creating music quotes
+(@ref{Quoting other voices}).
+
+Output definitions define the relation between contexts as well as
+their respective default settings. While most changes will
+usually be made inside of a @code{\layout} block, Midi-related
+settings will only have an effect when made within a @code{\midi}
+block.
+
+@funindex autoBeaming
+Some settings affect several outputs: for example, if
+@code{autoBeaming} is turned off in some context, beams count as
+melismata for the purpose of matching music to lyrics as described
+in @ref{Automatic syllable durations}. This matching is done both
+for printed output as well as for Midi. If changes made to
+@code{autoBeaming} within a context definition of a @code{\layout}
+block are not repeated in the corresponding @code{\midi} block,
+lyrics and music will get out of sync in Midi.
+
+@seealso
+Installed Files:
+@file{ly/engraver-init.ly}.
+@file{ly/performer-init.ly}.
+
@node Score - the master of all contexts
@unnumberedsubsubsec Score - the master of all contexts
across staves.
A Score context is instantiated implicitly when a
-@code{\score @{@dots{}@}} or @code{\layout @{@dots{}@}} block is
-processed.
+@code{\score @{@dots{}@}} block is processed.
@node Top-level contexts - staff containers
@unnumberedsubsubsec Top-level contexts - staff containers
@funindex \context
@funindex \layout
-The context settings which are to be used by default in
+The default context settings which are to be used for typesetting in
@code{Score}, @code{Staff}, @code{Voice} and other contexts may be
-specified in a @code{\context} block within any @code{\layout} block.
+specified in a @code{\context} block within any @code{\layout}
+block.
+
+Settings for Midi output as opposed to typesetting will have to be
+separately specified in @code{\midi} blocks (see @ref{Output
+definitions - blueprints for contexts}).
+
The @code{\layout} block should be placed within the @code{\score}
block to which it is to apply, after the music.
@}
@end example
+Since such a @q{context modification} is specified inside of
+music, it will affect @emph{all} outputs (typesetting @emph{and}
+Midi) as opposed to changes within an output definition.
+
The following types of settings may be specified:
@itemize
@item
otherwise the default value taken from the most recent appropriate
-@code{\context} block in the @code{\layout} blocks is used,
+@code{\context} block in the @code{\layout} or @code{\midi} blocks
+is used,
@item
otherwise the LilyPond built-in default is used.
@ref{Bottom-level contexts - voices},
@ref{The set command},
@ref{The override command},
-@ref{The \layout block}.
+@ref{The layout block,,The @code{@bs{}layout} block}.
@node Defining new contexts
\override Stem.transparent = ##t
@end example
-All these plug-ins have to cooperate, and this is achieved with a
-special plug-in, which must be marked with the keyword @code{\type}.
-This should always be @code{Engraver_group}.
+All these plug-ins have to communicate under the control of the
+context. The mechanisms with which contexts communicate are
+established by declaring the context @code{\type}. Within a
+@code{\layout} block, most contexts will be of type
+@code{Engraver_group}. Some special contexts and contexts in
+@code{\midi} blocks use other context types. Copying and
+modifying an existing context definition will also fill in the
+type. Since this example creates a definition from scratch, it
+needs to be specified explicitly.
@example
\type "Engraver_group"
@}
@end example
+To complete this example, changes affecting the context hierarchy
+should be repeated in a @code{\midi} block so that Midi output
+depends on the same context relations.
+
@seealso
Internals Reference:
rehearsal marks are aligned:
@lilypond[verbatim,quote,relative=1]
-% The rehearsal mark will be aligned to right edge of the Clef
+% The rehearsal mark will be aligned to the right edge of the Clef
\override Score.RehearsalMark.break-align-symbols = #'(clef)
\key a \major
\clef treble
\mark "↓"
e1
-% The rehearsal mark will be centered above the Time Signature
+% The rehearsal mark will be aligned to the left edge of the Time Signature
\override Score.RehearsalMark.break-align-symbols = #'(time-signature)
\key a \major
\clef treble
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