3.2.15 beam-interface (LilyPond Internals Reference)

#### 3.2.15 `beam-interface`

A beam.

The `beam-thickness` property is the weight of beams, measured in staffspace. The `direction` property is not user-serviceable. Use the `direction` property of `Stem` instead.

The following properties may be set in the `details` list.

`beam-eps`

  Epsilon for beam quant code to check for presence in gap.

`collision-padding`

  Padding value to avoid vertical collision with other objects.

`collision-penalty`

  Demerit penalty for `collision-padding`.

`damping-direction-penalty`

  Demerit penalty applied when beam direction is different from damping direction.

`hint-direction-penalty`

  Demerit penalty applied when beam direction is different from damping direction, but damping slope is <= `round-to-zero-slope`.

`ideal-slope-factor`

  Demerit scaling factor for difference between beam slope and damping slope.

`musical-direction-factor`

  Demerit scaling factor for difference between beam slope and music slope.

`region-size`

  Size of region for checking quant scores.

`round-to-zero-slope`

  Damping slope which is considered zero for purposes of calculating direction penalties.

`secondary-beam-demerit`

  Demerit used in quanting calculations for multiple beams.

`stem-collision-factor`

  Demerit factor used for colliding stems.

`stem-length-demerit-factor`

  Demerit factor used for inappropriate stem lengths.

`stem-length-limit-penalty`

  Penalty for differences in stem lengths on a beam.

#### User-settable properties:

> `accidental-padding` (number)

>   Property used by Beam to avoid accidentals in whole-note tremolos.

> `auto-knee-gap` (dimension, in staff space)

>   If a gap is found between note heads where a horizontal beam fits and it is larger than this number, make a kneed beam.

> `beam-thickness` (dimension, in staff space)

>   Beam thickness, measured in `staff-space` units.

> `beamed-stem-shorten` (list)

>   How much to shorten beamed stems, when their direction is forced. It is a list, since the value is different depending on the number of flags and beams.

> `beaming` (pair)

>   Pair of number lists. Each number list specifies which beams to make. `0` is the central beam, `1` is the next beam toward the note, etc. This information is used to determine how to connect the beaming patterns from stem to stem inside a beam.

> `break-overshoot` (pair of numbers)

>   A pair of numbers specifying how much a broken spanner sticks out of its bounds horizontally on the broken side(s). For broken beams and broken tuplet brackets, the bounds are given by the prefatory matter on the left and/or the rightmost column on the right. For broken horizontal brackets, the bounds are the leftmost and/or rightmost column; for broken measure spanners, the left and/or right edge of the staff.

> `clip-edges` (boolean)

>   Allow outward pointing beamlets at the edges of beams?

> `collision-interfaces` (list)

>   A list of interfaces for which automatic beam-collision resolution is run.

> `collision-voice-only` (boolean)

>   Avoid beam collisions only with grobs of the voice in which the beam was created.

> `concaveness` (number)

>   A beam is concave if its inner stems are closer to the beam than the two outside stems. This number is a measure of the closeness of the inner stems. It is used for damping the slope of the beam.

> `damping` (number)

>   Amount of beam slope damping.

> `details` (alist, with symbols as keys)

>   An alist of parameters for detailed grob behavior. See All layout objects for more information on the available parameters and their default values of a particular grob’s `details` property. See Graphical Object Interfaces for documentation of the available parameters. Supporting interfaces can be found at the bottom of a grob’s description section.

> `direction` (direction)

>   If `side-axis` is `0` (or `X`), then this property determines whether the object is placed `LEFT`, `CENTER` or `RIGHT` with respect to the other object. Otherwise, it determines whether the object is placed `UP`, `CENTER` or `DOWN`. Numerical values may also be used: `UP`=`1`, `DOWN`=`-1`, `LEFT`=`-1`, `RIGHT`=`1`, `CENTER`=`0`.

> `gap` (dimension, in staff space)

>   Size of a gap in a variable symbol.

> `gap-count` (integer)

>   Number of ‘floating’ beams in a two-stem tremolo.

> `grow-direction` (direction)

>   Crescendo or decrescendo?

> `inspect-quants` (pair of numbers)

>   If debugging is set, set beam and slur position to a (quantized) position that is as close as possible to this value, and print the demerits for the inspected position in the output.

> `knee` (boolean)

>   Is this beam kneed?

> `length-fraction` (number)

>   Multiplier for lengths. Used for determining ledger lines and stem lengths.

> `minimum-length` (dimension, in staff space)

>   Try to make a spanner at least this long, normally in the horizontal direction. This requires an appropriate callback for the `springs-and-rods` property. If added to a `Tie`, this sets the minimum distance between note heads.

> `neutral-direction` (direction)

>   Which direction to take in the center of the staff.

> `positions` (pair of numbers)

>   Pair of staff coordinates `(start . end)`, where start and end are vertical positions in `staff-space` units of the current staff. For slurs, this value selects which slur candidate to use; if extreme positions are requested, the closest one is taken.

> `skip-quanting` (boolean)

>   Should beam quanting be skipped?

> `X-positions` (pair of numbers)

>   Pair of X staff coordinates of a spanner in the form `(left . right)`, where both left and right are in `staff-space` units of the current staff.

#### Internal properties:

> `annotation` (string)

>   Annotate a grob for debug purposes.

> `beam-segments` (list)

>   Internal representation of beam segments.

> `covered-grobs` (array of grobs)

>   Grobs that could potentially collide with a beam.

> `least-squares-dy` (number)

>   The ideal beam slope, without damping.

> `normal-stems` (array of grobs)

>   An array of visible stems.

> `quantized-positions` (pair of numbers)

>   The beam positions after quanting.

> `shorten` (dimension, in staff space)

>   The amount of space that a stem is shortened. Internally used to distribute beam shortening over stems.

> `stems` (array of grobs)

>   An array of stem objects.

This grob interface is used in the following graphical object(s): `Beam`.

#### LilyPond Internals Reference v2.26.0 (stable-branch).

- 1 Music definitions
  - 1.1 Music expressions
    - 1.1.1 `AbsoluteDynamicEvent`
    - 1.1.2 `AdHocJumpEvent`
    - 1.1.3 `AdHocMarkEvent`
    - 1.1.4 `AlternativeEvent`
    - 1.1.5 `AnnotateOutputEvent`
    - 1.1.6 `ApplyContext`
    - 1.1.7 `ApplyOutputEvent`
    - 1.1.8 `ArpeggioEvent`
    - 1.1.9 `ArticulationEvent`
    - 1.1.10 `BarCheckEvent`
    - 1.1.11 `BarEvent`
    - 1.1.12 `BassFigureEvent`
    - 1.1.13 `BeamEvent`
    - 1.1.14 `BeamForbidEvent`
    - 1.1.15 `BendAfterEvent`
    - 1.1.16 `BendSpanEvent`
    - 1.1.17 `BreakDynamicSpanEvent`
    - 1.1.18 `BreathingEvent`
    - 1.1.19 `CaesuraEvent`
    - 1.1.20 `ChordSlurEvent`
    - 1.1.21 `ClusterNoteEvent`
    - 1.1.22 `CodaMarkEvent`
    - 1.1.23 `CompletizeExtenderEvent`
    - 1.1.24 `ContextChange`
    - 1.1.25 `ContextSpeccedMusic`
    - 1.1.26 `CrescendoEvent`
    - 1.1.27 `DalSegnoEvent`
    - 1.1.28 `DecrescendoEvent`
    - 1.1.29 `DoublePercentEvent`
    - 1.1.30 `DurationLineEvent`
    - 1.1.31 `EpisemaEvent`
    - 1.1.32 `Event`
    - 1.1.33 `EventChord`
    - 1.1.34 `ExtenderEvent`
    - 1.1.35 `FineEvent`
    - 1.1.36 `FingerGlideEvent`
    - 1.1.37 `FingeringEvent`
    - 1.1.38 `FootnoteEvent`
    - 1.1.39 `GlissandoEvent`
    - 1.1.40 `GraceMusic`
    - 1.1.41 `HarmonicEvent`
    - 1.1.42 `HyphenEvent`
    - 1.1.43 `InitialContextMusic`
    - 1.1.44 `KeyChangeEvent`
    - 1.1.45 `LabelEvent`
    - 1.1.46 `LaissezVibrerEvent`
    - 1.1.47 `LigatureEvent`
    - 1.1.48 `LineBreakEvent`
    - 1.1.49 `LyricCombineMusic`
    - 1.1.50 `LyricEvent`
    - 1.1.51 `MeasureCounterEvent`
    - 1.1.52 `MeasureSpannerEvent`
    - 1.1.53 `MultiMeasureArticulationEvent`
    - 1.1.54 `MultiMeasureRestEvent`
    - 1.1.55 `MultiMeasureRestMusic`
    - 1.1.56 `MultiMeasureTextEvent`
    - 1.1.57 `Music`
    - 1.1.58 `NonArpeggiatoEvent`
    - 1.1.59 `NoteEvent`
    - 1.1.60 `NoteGroupingEvent`
    - 1.1.61 `OptionalMaterialEvent`
    - 1.1.62 `OttavaEvent`
    - 1.1.63 `OverrideProperty`
    - 1.1.64 `PageBreakEvent`
    - 1.1.65 `PageTurnEvent`
    - 1.1.66 `PartCombineEvent`
    - 1.1.67 `PartCombineMusic`
    - 1.1.68 `PartialEvent`
    - 1.1.69 `PartialSet`
    - 1.1.70 `PercentEvent`
    - 1.1.71 `PercentRepeatedMusic`
    - 1.1.72 `PesOrFlexaEvent`
    - 1.1.73 `PhrasingSlurEvent`
    - 1.1.74 `PolymetricTimeSignatureEvent`
    - 1.1.75 `PolymetricTimeSignatureMusic`
    - 1.1.76 `PostEvents`
    - 1.1.77 `PropertySet`
    - 1.1.78 `PropertyUnset`
    - 1.1.79 `QuoteMusic`
    - 1.1.80 `ReferenceTimeSignatureEvent`
    - 1.1.81 `ReferenceTimeSignatureMusic`
    - 1.1.82 `RehearsalMarkEvent`
    - 1.1.83 `RelativeOctaveCheck`
    - 1.1.84 `RelativeOctaveMusic`
    - 1.1.85 `RepeatSlashEvent`
    - 1.1.86 `RepeatTieEvent`
    - 1.1.87 `RestEvent`
    - 1.1.88 `RevertProperty`
    - 1.1.89 `ScriptEvent`
    - 1.1.90 `SectionEvent`
    - 1.1.91 `SectionLabelEvent`
    - 1.1.92 `SegnoMarkEvent`
    - 1.1.93 `SegnoRepeatedMusic`
    - 1.1.94 `SequentialAlternativeMusic`
    - 1.1.95 `SequentialMusic`
    - 1.1.96 `SimultaneousMusic`
    - 1.1.97 `SkipEvent`
    - 1.1.98 `SkipMusic`
    - 1.1.99 `SkippedMusic`
    - 1.1.100 `SlurEvent`
    - 1.1.101 `SostenutoEvent`
    - 1.1.102 `SpacingSectionEvent`
    - 1.1.103 `SpanEvent`
    - 1.1.104 `StaffHighlightEvent`
    - 1.1.105 `StaffSpanEvent`
    - 1.1.106 `StringNumberEvent`
    - 1.1.107 `StrokeFingerEvent`
    - 1.1.108 `SustainEvent`
    - 1.1.109 `TempoChangeEvent`
    - 1.1.110 `TextMarkEvent`
    - 1.1.111 `TextScriptEvent`
    - 1.1.112 `TextSpanEvent`
    - 1.1.113 `TieEvent`
    - 1.1.114 `TimeScaledMusic`
    - 1.1.115 `TransposedMusic`
    - 1.1.116 `TremoloEvent`
    - 1.1.117 `TremoloRepeatedMusic`
    - 1.1.118 `TremoloSpanEvent`
    - 1.1.119 `TrillSpanEvent`
    - 1.1.120 `TupletSpanEvent`
    - 1.1.121 `UnaCordaEvent`
    - 1.1.122 `UnfoldedRepeatedMusic`
    - 1.1.123 `UnfoldedSpeccedMusic`
    - 1.1.124 `UnrelativableMusic`
    - 1.1.125 `VoiceSeparator`
    - 1.1.126 `VoltaRepeatEndEvent`
    - 1.1.127 `VoltaRepeatStartEvent`
    - 1.1.128 `VoltaRepeatedMusic`
    - 1.1.129 `VoltaSpanEvent`
    - 1.1.130 `VoltaSpeccedMusic`
    - 1.1.131 `VowelTransitionEvent`
  - 1.2 Music classes
    - 1.2.1 `absolute-dynamic-event`
    - 1.2.2 `ad-hoc-jump-event`
    - 1.2.3 `ad-hoc-mark-event`
    - 1.2.4 `alternative-event`
    - 1.2.5 `annotate-output-event`
    - 1.2.6 `apply-output-event`
    - 1.2.7 `arpeggio-event`
    - 1.2.8 `articulation-event`
    - 1.2.9 `bar-check-event`
    - 1.2.10 `bar-event`
    - 1.2.11 `bass-figure-event`
    - 1.2.12 `beam-event`
    - 1.2.13 `beam-forbid-event`
    - 1.2.14 `bend-after-event`
    - 1.2.15 `bend-span-event`
    - 1.2.16 `break-dynamic-span-event`
    - 1.2.17 `break-event`
    - 1.2.18 `break-span-event`
    - 1.2.19 `breathing-event`
    - 1.2.20 `caesura-event`
    - 1.2.21 `chord-slur-event`
    - 1.2.22 `cluster-note-event`
    - 1.2.23 `coda-mark-event`
    - 1.2.24 `completize-extender-event`
    - 1.2.25 `crescendo-event`
    - 1.2.26 `dal-segno-event`
    - 1.2.27 `decrescendo-event`
    - 1.2.28 `double-percent-event`
    - 1.2.29 `duration-line-event`
    - 1.2.30 `dynamic-event`
    - 1.2.31 `episema-event`
    - 1.2.32 `extender-event`
    - 1.2.33 `fine-event`
    - 1.2.34 `finger-glide-event`
    - 1.2.35 `fingering-event`
    - 1.2.36 `footnote-event`
    - 1.2.37 `general-rest-event`
    - 1.2.38 `glissando-event`
    - 1.2.39 `harmonic-event`
    - 1.2.40 `hyphen-event`
    - 1.2.41 `key-change-event`
    - 1.2.42 `label-event`
    - 1.2.43 `laissez-vibrer-event`
    - 1.2.44 `layout-instruction-event`
    - 1.2.45 `ligature-event`
    - 1.2.46 `line-break-event`
    - 1.2.47 `lyric-event`
    - 1.2.48 `mark-event`
    - 1.2.49 `measure-counter-event`
    - 1.2.50 `measure-spanner-event`
    - 1.2.51 `melodic-event`
    - 1.2.52 `multi-measure-articulation-event`
    - 1.2.53 `multi-measure-rest-event`
    - 1.2.54 `multi-measure-text-event`
    - 1.2.55 `music-event`
    - 1.2.56 `non-arpeggiato-event`
    - 1.2.57 `note-event`
    - 1.2.58 `note-grouping-event`
    - 1.2.59 `optional-material-event`
    - 1.2.60 `ottava-event`
    - 1.2.61 `page-break-event`
    - 1.2.62 `page-turn-event`
    - 1.2.63 `part-combine-event`
    - 1.2.64 `partial-event`
    - 1.2.65 `pedal-event`
    - 1.2.66 `percent-event`
    - 1.2.67 `pes-or-flexa-event`
    - 1.2.68 `phrasing-slur-event`
    - 1.2.69 `polymetric-time-signature-event`
    - 1.2.70 `reference-time-signature-event`
    - 1.2.71 `rehearsal-mark-event`
    - 1.2.72 `repeat-slash-event`
    - 1.2.73 `repeat-tie-event`
    - 1.2.74 `rest-event`
    - 1.2.75 `rhythmic-event`
    - 1.2.76 `script-event`
    - 1.2.77 `section-event`
    - 1.2.78 `section-label-event`
    - 1.2.79 `segno-mark-event`
    - 1.2.80 `skip-event`
    - 1.2.81 `slur-event`
    - 1.2.82 `sostenuto-event`
    - 1.2.83 `spacing-section-event`
    - 1.2.84 `span-dynamic-event`
    - 1.2.85 `span-event`
    - 1.2.86 `staff-highlight-event`
    - 1.2.87 `staff-span-event`
    - 1.2.88 `StreamEvent`
    - 1.2.89 `string-number-event`
    - 1.2.90 `stroke-finger-event`
    - 1.2.91 `structural-event`
    - 1.2.92 `sustain-event`
    - 1.2.93 `tempo-change-event`
    - 1.2.94 `text-mark-event`
    - 1.2.95 `text-script-event`
    - 1.2.96 `text-span-event`
    - 1.2.97 `tie-event`
    - 1.2.98 `time-signature-event`
    - 1.2.99 `tremolo-event`
    - 1.2.100 `tremolo-span-event`
    - 1.2.101 `trill-span-event`
    - 1.2.102 `tuplet-span-event`
    - 1.2.103 `una-corda-event`
    - 1.2.104 `volta-repeat-end-event`
    - 1.2.105 `volta-repeat-start-event`
    - 1.2.106 `volta-span-event`
    - 1.2.107 `vowel-transition-event`
  - 1.3 Music properties
- 2 Translation
  - 2.1 Contexts
    - 2.1.1 `ChoirStaff`
    - 2.1.2 `ChordGrid`
    - 2.1.3 `ChordGridScore`
    - 2.1.4 `ChordNames`
    - 2.1.5 `CueVoice`
    - 2.1.6 `Devnull`
    - 2.1.7 `DrumStaff`
    - 2.1.8 `DrumVoice`
    - 2.1.9 `Dynamics`
    - 2.1.10 `FiguredBass`
    - 2.1.11 `FretBoards`
    - 2.1.12 `Global`
    - 2.1.13 `GrandStaff`
    - 2.1.14 `GregorianTranscriptionLyrics`
    - 2.1.15 `GregorianTranscriptionStaff`
    - 2.1.16 `GregorianTranscriptionVoice`
    - 2.1.17 `InternalGregorianStaff`
    - 2.1.18 `InternalMensuralStaff`
    - 2.1.19 `KievanStaff`
    - 2.1.20 `KievanVoice`
    - 2.1.21 `Lyrics`
    - 2.1.22 `MensuralStaff`
    - 2.1.23 `MensuralVoice`
    - 2.1.24 `NoteNames`
    - 2.1.25 `NullVoice`
    - 2.1.26 `OneStaff`
    - 2.1.27 `PetrucciStaff`
    - 2.1.28 `PetrucciVoice`
    - 2.1.29 `PianoStaff`
    - 2.1.30 `RhythmicStaff`
    - 2.1.31 `Score`
    - 2.1.32 `Staff`
    - 2.1.33 `StaffGroup`
    - 2.1.34 `StandaloneRhythmScore`
    - 2.1.35 `StandaloneRhythmStaff`
    - 2.1.36 `StandaloneRhythmVoice`
    - 2.1.37 `TabStaff`
    - 2.1.38 `TabVoice`
    - 2.1.39 `VaticanaLyrics`
    - 2.1.40 `VaticanaScore`
    - 2.1.41 `VaticanaStaff`
    - 2.1.42 `VaticanaVoice`
    - 2.1.43 `Voice`
  - 2.2 Engravers and Performers
    - 2.2.1 `Accidental_engraver`
    - 2.2.2 `Alteration_glyph_engraver`
    - 2.2.3 `Ambitus_engraver`
    - 2.2.4 `Apply_output_engraver`
    - 2.2.5 `Arpeggio_engraver`
    - 2.2.6 `Auto_beam_engraver`
    - 2.2.7 `Axis_group_engraver`
    - 2.2.8 `Balloon_engraver`
    - 2.2.9 `Bar_engraver`
    - 2.2.10 `Bar_number_engraver`
    - 2.2.11 `Beam_collision_engraver`
    - 2.2.12 `Beam_engraver`
    - 2.2.13 `Beam_performer`
    - 2.2.14 `Beat_engraver`
    - 2.2.15 `Beat_performer`
    - 2.2.16 `Bend_engraver`
    - 2.2.17 `Bend_spanner_engraver`
    - 2.2.18 `Break_align_engraver`
    - 2.2.19 `Breathing_sign_engraver`
    - 2.2.20 `Caesura_engraver`
    - 2.2.21 `Centered_bar_number_align_engraver`
    - 2.2.22 `Chord_name_engraver`
    - 2.2.23 `Chord_square_engraver`
    - 2.2.24 `Chord_tremolo_engraver`
    - 2.2.25 `Clef_engraver`
    - 2.2.26 `Cluster_spanner_engraver`
    - 2.2.27 `Collision_engraver`
    - 2.2.28 `Completion_heads_engraver`
    - 2.2.29 `Completion_rest_engraver`
    - 2.2.30 `Concurrent_hairpin_engraver`
    - 2.2.31 `Control_track_performer`
    - 2.2.32 `Cue_clef_engraver`
    - 2.2.33 `Current_chord_text_engraver`
    - 2.2.34 `Custos_engraver`
    - 2.2.35 `Divisio_engraver`
    - 2.2.36 `Dot_column_engraver`
    - 2.2.37 `Dots_engraver`
    - 2.2.38 `Double_percent_repeat_engraver`
    - 2.2.39 `Drum_note_performer`
    - 2.2.40 `Drum_notes_engraver`
    - 2.2.41 `Duration_line_engraver`
    - 2.2.42 `Dynamic_align_engraver`
    - 2.2.43 `Dynamic_engraver`
    - 2.2.44 `Dynamic_performer`
    - 2.2.45 `Episema_engraver`
    - 2.2.46 `Extender_engraver`
    - 2.2.47 `Figured_bass_engraver`
    - 2.2.48 `Figured_bass_position_engraver`
    - 2.2.49 `Finger_glide_engraver`
    - 2.2.50 `Fingering_column_engraver`
    - 2.2.51 `Fingering_engraver`
    - 2.2.52 `Font_size_engraver`
    - 2.2.53 `Footnote_engraver`
    - 2.2.54 `Forbid_line_break_engraver`
    - 2.2.55 `Fretboard_engraver`
    - 2.2.56 `Glissando_engraver`
    - 2.2.57 `Grace_auto_beam_engraver`
    - 2.2.58 `Grace_beam_engraver`
    - 2.2.59 `Grace_engraver`
    - 2.2.60 `Grace_spacing_engraver`
    - 2.2.61 `Grid_chord_name_engraver`
    - 2.2.62 `Grid_line_span_engraver`
    - 2.2.63 `Grid_point_engraver`
    - 2.2.64 `Grob_pq_engraver`
    - 2.2.65 `Horizontal_bracket_engraver`
    - 2.2.66 `Horizontal_script_engraver`
    - 2.2.67 `Hyphen_engraver`
    - 2.2.68 `Instrument_name_engraver`
    - 2.2.69 `Instrument_switch_engraver`
    - 2.2.70 `Jump_engraver`
    - 2.2.71 `Keep_alive_together_engraver`
    - 2.2.72 `Key_engraver`
    - 2.2.73 `Key_performer`
    - 2.2.74 `Kievan_ligature_engraver`
    - 2.2.75 `Laissez_vibrer_engraver`
    - 2.2.76 `Ledger_line_engraver`
    - 2.2.77 `Ligature_bracket_engraver`
    - 2.2.78 `Lyric_engraver`
    - 2.2.79 `Lyric_performer`
    - 2.2.80 `Lyric_repeat_count_engraver`
    - 2.2.81 `Mark_engraver`
    - 2.2.82 `Mark_performer`
    - 2.2.83 `Mark_tracking_translator`
    - 2.2.84 `Measure_counter_engraver`
    - 2.2.85 `Measure_grouping_engraver`
    - 2.2.86 `Measure_spanner_engraver`
    - 2.2.87 `Melody_engraver`
    - 2.2.88 `Mensural_ligature_engraver`
    - 2.2.89 `Merge_mmrest_numbers_engraver`
    - 2.2.90 `Merge_rests_engraver`
    - 2.2.91 `Metronome_mark_engraver`
    - 2.2.92 `Midi_control_change_performer`
    - 2.2.93 `Multi_measure_rest_engraver`
    - 2.2.94 `New_fingering_engraver`
    - 2.2.95 `Non_musical_script_column_engraver`
    - 2.2.96 `Note_head_line_engraver`
    - 2.2.97 `Note_heads_engraver`
    - 2.2.98 `Note_name_engraver`
    - 2.2.99 `Note_performer`
    - 2.2.100 `Note_spacing_engraver`
    - 2.2.101 `Optional_material_bracket_engraver`
    - 2.2.102 `Ottava_spanner_engraver`
    - 2.2.103 `Page_turn_engraver`
    - 2.2.104 `Paper_column_engraver`
    - 2.2.105 `Parenthesis_engraver`
    - 2.2.106 `Part_combine_engraver`
    - 2.2.107 `Percent_repeat_engraver`
    - 2.2.108 `Phrasing_slur_engraver`
    - 2.2.109 `Piano_pedal_align_engraver`
    - 2.2.110 `Piano_pedal_engraver`
    - 2.2.111 `Piano_pedal_performer`
    - 2.2.112 `Pitch_squash_engraver`
    - 2.2.113 `Pitched_trill_engraver`
    - 2.2.114 `Pure_from_neighbor_engraver`
    - 2.2.115 `Repeat_acknowledge_engraver`
    - 2.2.116 `Repeat_tie_engraver`
    - 2.2.117 `Rest_collision_engraver`
    - 2.2.118 `Rest_engraver`
    - 2.2.119 `Rhythmic_column_engraver`
    - 2.2.120 `Script_column_engraver`
    - 2.2.121 `Script_engraver`
    - 2.2.122 `Script_row_engraver`
    - 2.2.123 `Separating_line_group_engraver`
    - 2.2.124 `Show_control_points_engraver`
    - 2.2.125 `Signum_repetitionis_engraver`
    - 2.2.126 `Skip_typesetting_engraver`
    - 2.2.127 `Slash_repeat_engraver`
    - 2.2.128 `Slur_engraver`
    - 2.2.129 `Slur_performer`
    - 2.2.130 `Spacing_engraver`
    - 2.2.131 `Span_arpeggio_engraver`
    - 2.2.132 `Span_bar_engraver`
    - 2.2.133 `Span_bar_stub_engraver`
    - 2.2.134 `Span_stem_engraver`
    - 2.2.135 `Spanner_break_forbid_engraver`
    - 2.2.136 `Spanner_tracking_engraver`
    - 2.2.137 `Staff_collecting_engraver`
    - 2.2.138 `Staff_highlight_engraver`
    - 2.2.139 `Staff_performer`
    - 2.2.140 `Staff_symbol_engraver`
    - 2.2.141 `Stanza_number_align_engraver`
    - 2.2.142 `Stanza_number_engraver`
    - 2.2.143 `Stem_engraver`
    - 2.2.144 `System_start_delimiter_engraver`
    - 2.2.145 `Tab_note_heads_engraver`
    - 2.2.146 `Tab_staff_symbol_engraver`
    - 2.2.147 `Tab_tie_follow_engraver`
    - 2.2.148 `Tempo_performer`
    - 2.2.149 `Text_engraver`
    - 2.2.150 `Text_mark_engraver`
    - 2.2.151 `Text_spanner_engraver`
    - 2.2.152 `Tie_engraver`
    - 2.2.153 `Tie_performer`
    - 2.2.154 `Time_signature_engraver`
    - 2.2.155 `Time_signature_performer`
    - 2.2.156 `Timing_translator`
    - 2.2.157 `Toe_heel_engraver`
    - 2.2.158 `Trill_spanner_engraver`
    - 2.2.159 `Tuplet_engraver`
    - 2.2.160 `Tweak_engraver`
    - 2.2.161 `Vaticana_ligature_engraver`
    - 2.2.162 `Vertical_align_engraver`
    - 2.2.163 `Volta_engraver`
  - 2.3 Tunable context properties
  - 2.4 Internal context properties
- 3 Backend
  - 3.1 All layout objects
    - 3.1.1 `Accidental`
    - 3.1.2 `AccidentalCautionary`
    - 3.1.3 `AccidentalPlacement`
    - 3.1.4 `AccidentalSuggestion`
    - 3.1.5 `Ambitus`
    - 3.1.6 `AmbitusAccidental`
    - 3.1.7 `AmbitusLine`
    - 3.1.8 `AmbitusNoteHead`
    - 3.1.9 `ApproximatePitchNoteHead`
    - 3.1.10 `Arpeggio`
    - 3.1.11 `BalloonText`
    - 3.1.12 `BarLine`
    - 3.1.13 `BarNumber`
    - 3.1.14 `BassFigure`
    - 3.1.15 `BassFigureAlignment`
    - 3.1.16 `BassFigureAlignmentPositioning`
    - 3.1.17 `BassFigureBracket`
    - 3.1.18 `BassFigureContinuation`
    - 3.1.19 `BassFigureLine`
    - 3.1.20 `Beam`
    - 3.1.21 `BendAfter`
    - 3.1.22 `BendSpanner`
    - 3.1.23 `BreakAlignGroup`
    - 3.1.24 `BreakAlignment`
    - 3.1.25 `BreathingSign`
    - 3.1.26 `CaesuraScript`
    - 3.1.27 `CenteredBarNumber`
    - 3.1.28 `CenteredBarNumberLineSpanner`
    - 3.1.29 `ChordBracket`
    - 3.1.30 `ChordName`
    - 3.1.31 `ChordSlur`
    - 3.1.32 `ChordSquare`
    - 3.1.33 `Clef`
    - 3.1.34 `ClefModifier`
    - 3.1.35 `ClusterSpanner`
    - 3.1.36 `ClusterSpannerBeacon`
    - 3.1.37 `CodaMark`
    - 3.1.38 `CombineTextScript`
    - 3.1.39 `ControlPoint`
    - 3.1.40 `ControlPolygon`
    - 3.1.41 `CueClef`
    - 3.1.42 `CueEndClef`
    - 3.1.43 `Custos`
    - 3.1.44 `Divisio`
    - 3.1.45 `DotColumn`
    - 3.1.46 `Dots`
    - 3.1.47 `DoublePercentRepeat`
    - 3.1.48 `DoublePercentRepeatCounter`
    - 3.1.49 `DoubleRepeatSlash`
    - 3.1.50 `DurationLine`
    - 3.1.51 `DynamicLineSpanner`
    - 3.1.52 `DynamicText`
    - 3.1.53 `DynamicTextSpanner`
    - 3.1.54 `Episema`
    - 3.1.55 `FingerGlideSpanner`
    - 3.1.56 `Fingering`
    - 3.1.57 `FingeringColumn`
    - 3.1.58 `Flag`
    - 3.1.59 `Footnote`
    - 3.1.60 `FretBoard`
    - 3.1.61 `Glissando`
    - 3.1.62 `GraceSpacing`
    - 3.1.63 `GridChordName`
    - 3.1.64 `GridLine`
    - 3.1.65 `GridPoint`
    - 3.1.66 `Hairpin`
    - 3.1.67 `HorizontalBracket`
    - 3.1.68 `HorizontalBracketText`
    - 3.1.69 `InstrumentName`
    - 3.1.70 `InstrumentSwitch`
    - 3.1.71 `JumpScript`
    - 3.1.72 `KeyCancellation`
    - 3.1.73 `KeySignature`
    - 3.1.74 `KievanLigature`
    - 3.1.75 `LaissezVibrerTie`
    - 3.1.76 `LaissezVibrerTieColumn`
    - 3.1.77 `LedgerLineSpanner`
    - 3.1.78 `LeftEdge`
    - 3.1.79 `LigatureBracket`
    - 3.1.80 `LyricExtender`
    - 3.1.81 `LyricHyphen`
    - 3.1.82 `LyricRepeatCount`
    - 3.1.83 `LyricSpace`
    - 3.1.84 `LyricText`
    - 3.1.85 `MeasureCounter`
    - 3.1.86 `MeasureGrouping`
    - 3.1.87 `MeasureSpanner`
    - 3.1.88 `MelodyItem`
    - 3.1.89 `MensuralLigature`
    - 3.1.90 `MetronomeMark`
    - 3.1.91 `MultiMeasureRest`
    - 3.1.92 `MultiMeasureRestNumber`
    - 3.1.93 `MultiMeasureRestScript`
    - 3.1.94 `MultiMeasureRestText`
    - 3.1.95 `NonMusicalPaperColumn`
    - 3.1.96 `NoteCollision`
    - 3.1.97 `NoteColumn`
    - 3.1.98 `NoteHead`
    - 3.1.99 `NoteName`
    - 3.1.100 `NoteSpacing`
    - 3.1.101 `OptionalMaterialBracket`
    - 3.1.102 `OttavaBracket`
    - 3.1.103 `PaperColumn`
    - 3.1.104 `Parentheses`
    - 3.1.105 `PercentRepeat`
    - 3.1.106 `PercentRepeatCounter`
    - 3.1.107 `PhrasingSlur`
    - 3.1.108 `PianoPedalBracket`
    - 3.1.109 `RehearsalMark`
    - 3.1.110 `RepeatSlash`
    - 3.1.111 `RepeatTie`
    - 3.1.112 `RepeatTieColumn`
    - 3.1.113 `Rest`
    - 3.1.114 `RestCollision`
    - 3.1.115 `Script`
    - 3.1.116 `ScriptColumn`
    - 3.1.117 `ScriptRow`
    - 3.1.118 `SectionLabel`
    - 3.1.119 `SegnoMark`
    - 3.1.120 `SignumRepetitionis`
    - 3.1.121 `Slur`
    - 3.1.122 `SostenutoPedal`
    - 3.1.123 `SostenutoPedalLineSpanner`
    - 3.1.124 `SpacingSpanner`
    - 3.1.125 `SpanBar`
    - 3.1.126 `SpanBarStub`
    - 3.1.127 `StaffEllipsis`
    - 3.1.128 `StaffGrouper`
    - 3.1.129 `StaffHighlight`
    - 3.1.130 `StaffSpacing`
    - 3.1.131 `StaffSymbol`
    - 3.1.132 `StanzaNumber`
    - 3.1.133 `Stem`
    - 3.1.134 `StemStub`
    - 3.1.135 `StemTremolo`
    - 3.1.136 `StringNumber`
    - 3.1.137 `StrokeFinger`
    - 3.1.138 `SustainPedal`
    - 3.1.139 `SustainPedalLineSpanner`
    - 3.1.140 `System`
    - 3.1.141 `SystemStartBar`
    - 3.1.142 `SystemStartBrace`
    - 3.1.143 `SystemStartBracket`
    - 3.1.144 `SystemStartSquare`
    - 3.1.145 `TabNoteHead`
    - 3.1.146 `TextMark`
    - 3.1.147 `TextScript`
    - 3.1.148 `TextSpanner`
    - 3.1.149 `Tie`
    - 3.1.150 `TieColumn`
    - 3.1.151 `TimeSignature`
    - 3.1.152 `TrillPitchAccidental`
    - 3.1.153 `TrillPitchGroup`
    - 3.1.154 `TrillPitchHead`
    - 3.1.155 `TrillPitchParentheses`
    - 3.1.156 `TrillSpanner`
    - 3.1.157 `TupletBracket`
    - 3.1.158 `TupletNumber`
    - 3.1.159 `UnaCordaPedal`
    - 3.1.160 `UnaCordaPedalLineSpanner`
    - 3.1.161 `VaticanaLigature`
    - 3.1.162 `VerticalAlignment`
    - 3.1.163 `VerticalAxisGroup`
    - 3.1.164 `VoiceFollower`
    - 3.1.165 `VoltaBracket`
    - 3.1.166 `VoltaBracketSpanner`
    - 3.1.167 `VowelTransition`
  - 3.2 Graphical Object Interfaces
    - 3.2.1 `accidental-interface`
    - 3.2.2 `accidental-participating-head-interface`
    - 3.2.3 `accidental-placement-interface`
    - 3.2.4 `accidental-suggestion-interface`
    - 3.2.5 `accidental-switch-interface`
    - 3.2.6 `align-interface`
    - 3.2.7 `ambitus-interface`
    - 3.2.8 `arpeggio-interface`
    - 3.2.9 `axis-group-interface`
    - 3.2.10 `balloon-interface`
    - 3.2.11 `bar-line-interface`
    - 3.2.12 `bar-number-interface`
    - 3.2.13 `bass-figure-alignment-interface`
    - 3.2.14 `bass-figure-interface`
    - 3.2.15 `beam-interface`
    - 3.2.16 `bend-after-interface`
    - 3.2.17 `bend-interface`
    - 3.2.18 `bezier-curve-interface`
    - 3.2.19 `break-alignable-interface`
    - 3.2.20 `break-aligned-interface`
    - 3.2.21 `break-alignment-interface`
    - 3.2.22 `breathing-sign-interface`
    - 3.2.23 `caesura-script-interface`
    - 3.2.24 `centered-bar-number-interface`
    - 3.2.25 `centered-bar-number-line-spanner-interface`
    - 3.2.26 `centered-spanner-interface`
    - 3.2.27 `chord-bracket-interface`
    - 3.2.28 `chord-name-interface`
    - 3.2.29 `chord-slur-interface`
    - 3.2.30 `chord-square-interface`
    - 3.2.31 `clef-interface`
    - 3.2.32 `clef-modifier-interface`
    - 3.2.33 `cluster-beacon-interface`
    - 3.2.34 `cluster-interface`
    - 3.2.35 `coda-mark-interface`
    - 3.2.36 `control-point-interface`
    - 3.2.37 `control-polygon-interface`
    - 3.2.38 `custos-interface`
    - 3.2.39 `dot-column-interface`
    - 3.2.40 `dots-interface`
    - 3.2.41 `duration-line-interface`
    - 3.2.42 `dynamic-interface`
    - 3.2.43 `dynamic-line-spanner-interface`
    - 3.2.44 `dynamic-text-interface`
    - 3.2.45 `dynamic-text-spanner-interface`
    - 3.2.46 `enclosing-bracket-interface`
    - 3.2.47 `episema-interface`
    - 3.2.48 `figured-bass-continuation-interface`
    - 3.2.49 `finger-glide-interface`
    - 3.2.50 `finger-interface`
    - 3.2.51 `fingering-column-interface`
    - 3.2.52 `flag-interface`
    - 3.2.53 `font-interface`
    - 3.2.54 `footnote-interface`
    - 3.2.55 `fret-diagram-interface`
    - 3.2.56 `glissando-interface`
    - 3.2.57 `grace-spacing-interface`
    - 3.2.58 `gregorian-ligature-interface`
    - 3.2.59 `grid-chord-name-interface`
    - 3.2.60 `grid-line-interface`
    - 3.2.61 `grid-point-interface`
    - 3.2.62 `grob-interface`
    - 3.2.63 `hairpin-interface`
    - 3.2.64 `hara-kiri-group-spanner-interface`
    - 3.2.65 `horizontal-bracket-interface`
    - 3.2.66 `horizontal-bracket-text-interface`
    - 3.2.67 `horizontal-line-spanner-interface`
    - 3.2.68 `inline-accidental-interface`
    - 3.2.69 `instrument-specific-markup-interface`
    - 3.2.70 `item-interface`
    - 3.2.71 `jump-script-interface`
    - 3.2.72 `key-cancellation-interface`
    - 3.2.73 `key-signature-interface`
    - 3.2.74 `kievan-ligature-interface`
    - 3.2.75 `ledger-line-spanner-interface`
    - 3.2.76 `ledgered-grob-interface`
    - 3.2.77 `ledgered-interface`
    - 3.2.78 `ligature-bracket-interface`
    - 3.2.79 `ligature-head-interface`
    - 3.2.80 `ligature-interface`
    - 3.2.81 `line-interface`
    - 3.2.82 `line-spanner-interface`
    - 3.2.83 `lyric-extender-interface`
    - 3.2.84 `lyric-hyphen-interface`
    - 3.2.85 `lyric-interface`
    - 3.2.86 `lyric-repeat-count-interface`
    - 3.2.87 `lyric-space-interface`
    - 3.2.88 `lyric-syllable-interface`
    - 3.2.89 `mark-interface`
    - 3.2.90 `measure-counter-interface`
    - 3.2.91 `measure-grouping-interface`
    - 3.2.92 `measure-spanner-interface`
    - 3.2.93 `melody-spanner-interface`
    - 3.2.94 `mensural-ligature-interface`
    - 3.2.95 `metronome-mark-interface`
    - 3.2.96 `multi-measure-interface`
    - 3.2.97 `multi-measure-rest-interface`
    - 3.2.98 `multi-measure-rest-number-interface`
    - 3.2.99 `musical-paper-column-interface`
    - 3.2.100 `non-musical-paper-column-interface`
    - 3.2.101 `note-collision-interface`
    - 3.2.102 `note-column-interface`
    - 3.2.103 `note-head-interface`
    - 3.2.104 `note-name-interface`
    - 3.2.105 `note-spacing-interface`
    - 3.2.106 `number-interface`
    - 3.2.107 `optional-material-bracket-interface`
    - 3.2.108 `ottava-bracket-interface`
    - 3.2.109 `outside-staff-axis-group-interface`
    - 3.2.110 `outside-staff-interface`
    - 3.2.111 `paper-column-interface`
    - 3.2.112 `parentheses-interface`
    - 3.2.113 `passage-delimiter-interface`
    - 3.2.114 `percent-repeat-interface`
    - 3.2.115 `piano-pedal-bracket-interface`
    - 3.2.116 `piano-pedal-interface`
    - 3.2.117 `piano-pedal-script-interface`
    - 3.2.118 `pitched-trill-interface`
    - 3.2.119 `pure-from-neighbor-interface`
    - 3.2.120 `rehearsal-mark-interface`
    - 3.2.121 `rest-collision-interface`
    - 3.2.122 `rest-interface`
    - 3.2.123 `rhythmic-grob-interface`
    - 3.2.124 `rhythmic-head-interface`
    - 3.2.125 `script-column-interface`
    - 3.2.126 `script-interface`
    - 3.2.127 `section-label-interface`
    - 3.2.128 `segno-mark-interface`
    - 3.2.129 `self-alignment-interface`
    - 3.2.130 `semi-tie-column-interface`
    - 3.2.131 `semi-tie-interface`
    - 3.2.132 `separation-item-interface`
    - 3.2.133 `side-position-interface`
    - 3.2.134 `signum-repetitionis-interface`
    - 3.2.135 `slur-interface`
    - 3.2.136 `spaceable-grob-interface`
    - 3.2.137 `spacing-interface`
    - 3.2.138 `spacing-options-interface`
    - 3.2.139 `spacing-spanner-interface`
    - 3.2.140 `span-bar-interface`
    - 3.2.141 `span-bar-stub-interface`
    - 3.2.142 `spanner-interface`
    - 3.2.143 `staff-ellipsis-interface`
    - 3.2.144 `staff-grouper-interface`
    - 3.2.145 `staff-highlight-interface`
    - 3.2.146 `staff-spacing-interface`
    - 3.2.147 `staff-symbol-interface`
    - 3.2.148 `staff-symbol-referencer-interface`
    - 3.2.149 `stanza-number-interface`
    - 3.2.150 `stem-interface`
    - 3.2.151 `stem-tremolo-interface`
    - 3.2.152 `sticky-grob-interface`
    - 3.2.153 `string-number-interface`
    - 3.2.154 `stroke-finger-interface`
    - 3.2.155 `system-interface`
    - 3.2.156 `system-start-delimiter-interface`
    - 3.2.157 `system-start-text-interface`
    - 3.2.158 `tab-note-head-interface`
    - 3.2.159 `text-interface`
    - 3.2.160 `text-mark-interface`
    - 3.2.161 `text-script-interface`
    - 3.2.162 `tie-column-interface`
    - 3.2.163 `tie-interface`
    - 3.2.164 `time-signature-interface`
    - 3.2.165 `trill-pitch-accidental-interface`
    - 3.2.166 `trill-spanner-interface`
    - 3.2.167 `tuplet-bracket-interface`
    - 3.2.168 `tuplet-number-interface`
    - 3.2.169 `unbreakable-spanner-interface`
    - 3.2.170 `vaticana-ligature-interface`
    - 3.2.171 `volta-bracket-interface`
    - 3.2.172 `volta-interface`
  - 3.3 User backend properties
  - 3.4 Internal backend properties
- 4 Scheme functions
- Appendix A Indices
  - A.1 Function index