2Shared Concepts in MEI

This chapter describes basic principles and shared concepts of MEI. Besides giving a general understanding of the basic structures of an MEI file it tries to introduce elements, models, and attributes that are part of the MEI.shared module, describe their use or at least point to chapters of these guidelines or tutorials that describe their use and application.

2.1Structural Elements

Besides elements used by multiple other modules the MEI.shared module defines the main structural elements of an MEI file. Please be aware that there is also a A short tutorial about the basics of XML & MEI that helps understanding and learning the contents of this chapter.

2.1.1Document Root Elements

MEI defines four elements qualifying as root elements (i.e. the element containing everything else) of an MEI document; the most common of these are defined in the MEI.shared module:

Contains a single MEI-conformant document, consisting of an MEI header and a musical text, either in isolation or as part of an meiCorpus element.

The most straightforward – and probably the most common choice fitting most of the use cases when encoding music – is the mei element. It contains an meiHead element for capturing metadata and a music element for describing the musical text. A more detailed description of the application of music can be found in the course of this section (see 2.1.2 General Music Structure Elements). If you want to learn more about the use of the meiHead element – formally declared in the MEI.header module – please visit the chapter 3.2 Structure of the MEI Header in the 3 Metadata in MEI section.

The below example shows the basic structure of an MEI file with mei as root element. Please be aware that this example still does not represent a valid MEI file:

<mei>
<meiHead>
<!-- metadata goes here -->
</meiHead>
<music>
<!-- description of musical text goes here -->
</music>
</mei>
Listing 4.

The other potential root elements serve different usecases or purposes.

Contains a single musical text of any kind, whether unitary or composite, for example, an etude, opera, song cycle, symphony, or anthology of piano solos.

A document with music as root element provides music notation markup without metadata, and could serve embedding MEI within other kinds of markup, e.g. TEI (see 14.1 TEI).

The below example shows the basic structure of an MEI file with music as root element. Basically this already represents a valid MEI file, although without any contents:

<music>
<!-- description of musical text goes here -->
</music>
Listing 5.

(MEI corpus) – A group of related MEI documents, consisting of a header for the group, and one or more elements, each with its own complete header.

meiCorpus contains an meiHead element describing a collection of related MEI-encoded texts – known as a corpus – and an mei element for each text. Further information regarding the organization and encoding of music corpora is given in chapter 3.8.5 Musical Corpora.

The below example shows the basic structure of an MEI file with meiCorpus as root element. Please be aware that this example still does not represent a valid MEI file:

<meiCorpus>
<meiHead>
<!-- metadata on the corpus goes here -->
</meiHead>
<mei>
<meiHead>
<!-- metadata on first text goes here -->
</meiHead>
<music>
<!-- description of first musical text goes here -->
</music>
</mei>
<mei>
<meiHead>
<!-- metadata on second text goes here -->
</meiHead>
<music>
<!-- description of second musical text goes here -->
</music>
</mei>
<mei>
<meiHead>
<!-- metadata on … text goes here -->
</meiHead>
<music>
<!-- description of … musical text goes here -->
</music>
</mei>
</meiCorpus>
Listing 6.

(MEI header) – Supplies the descriptive and declarative metadata prefixed to every MEI-conformant text.

The meiHead element, formally declared in the MEI.header module, is described in chapter 3.2 Structure of the MEI Header. A document with meiHead as root element only contains metadata and is also known as an independent or stand-alone header. Stand-alone headers are more fully described in chapter 3.8.1 Independent Headers.

The below example shows the basic structure of an MEI file with meiHead as root element. Please be aware that this example still does not represent a valid MEI file:

<meiHead>
<!-- metadata goes here -->
</meiHead>
Listing 7.

The above examples all carry two attributes on their root elements. While the @xmlns is a general feature of XML and not defined in MEI it is crucial for stating the fact that it is an MEI file you are dealing with. The second attribute is att.meiVersion.

@
meiversion (att.meiVersion)
Specifies a generic MEI version label.

Although not required the att.meiVersion attribute is important for defining a stable reference to a specific MEI-version used in the enclosed encoding, and thus is highly recommended on your root element.

2.1.2General Music Structure Elements

Contains a single musical text of any kind, whether unitary or composite, for example, an etude, opera, song cycle, symphony, or anthology of piano solos.

As indicated above, the general place for encoding the musical text is the music element. MEI.shared offers two possible child elements:

Contains the whole of a single musical text, excluding any front or back matter.
Contains a composite musical text, grouping together a sequence of distinct musical texts (or groups of such musical texts) which are regarded as a unit for some purpose, for example, the collected works of a composer.

While body holds the contents of a single musical text, group allows the textual body to consists of a series of (subordinate) musical texts or other e.g. to represent a collection of independent musical texts which is to be regarded as a single unit for processing or other purposes. It is provided to simplify the encoding of collections, anthologies, and cyclic works. It can also be used to record the potentially complex internal structure of corpora, covered more fully in chapter 3.8.5 Musical Corpora. Whether the musical text being encoded should be structured one way or the other is not to be decided here. For example, a collection of songs might be regarded as a single item in some circumstances, or as a number of distinct items in others. In such borderline cases, the encoder must choose whether to treat the text as unitary or composite; each option may have advantages and disadvantages.

There are several more possible child elements of the music element defined in other modules of MEI, such as front and back elements (defined in MEI.text module, cf. 9.2 Text in MEI), performance (defined in MEI.performance module, cf. 12.2 Performances), genDesc (defined in MEI.genetic module, cf. 11.3 Genetic Markup), facsimile (defined in MEI.facsimile module, cf. 12.1 Facsimiles).

Please be aware that the following examples still do not reflect valid MEI files as they are missing some required elements not defined in the MEI.shared module.

The basic structure of a unitary musical text:

<mei>
<meiHead>
<!-- metadata goes here -->
</meiHead>
<music>
<front>
<!-- front matter of text, if any, goes here -->
</front>
<body>
<!-- body of text goes here -->
</body>
<back>
<!-- back matter of text, if any, goes here -->
</back>
</music>
</mei>
Listing 8.

Examples of composite texts which may be represented using the group element include anthologies and other collections. The presence of common front matter referring to the whole collection, possibly in addition to front matter relating to each individual musical text, is a good indication that a given musical text might usefully be encoded in this way.

For example, the overall structure of a collection of songs might be encoded as follows:

<music>
<group>
<music>
<!-- song 1 -->
</music>
<music>
<!-- song 2 -->
</music>
<!-- additional songs here -->
</group>
</music>
Listing 9.

A group of musical texts may contain other unitary and grouped texts:

<music>
<group>
<music>
<!-- song 1 -->
</music>
<group>
<!-- songs sharing one or more characteristics, treated as a group -->
<music>
<!-- song 2 -->
</music>
<music>
<!-- song 3 -->
</music>
</group>
</group>
</music>
Listing 10.

The group element may be used to encode any kind of collection in which the constituents are regarded by the encoder as works in their own right, such as ad hoc single- or multiple-composer collections or anthologies of works not originally conceived of as a single composition.

2.1.2.1Divisions of the Body

This section describes sub-division of the body of a musical text. Front and back matter are described in chapter 9.2 Text in MEI.

(musical division) – Contains a subdivision of the body of a musical text.
@
type (att.typed)
Designation which characterizes the element in some sense, using any convenient classification scheme or typology that employs single-token labels.
@
class (att.classed)
Contains one or more URIs which denote classification terms that apply to the entity bearing this attribute.

The body of a unitary musical text may contain one or more discrete, linear segments. The names commonly used for these structural subdivisions vary with the genre, style, and time period of the music, or even at the whim of the author, editor, or publisher. For example, a major subdivision of a symphony is generally referred to as a ‘movement’. An opera, on the other hand, is usually organized into ‘acts’ and then further by ‘scenes’. All such divisions are treated as occurrences of the same neutrally-named mdiv element. The attributes type or class may be used to categorize them independently of their hierarchic level.

To accommodate "divisions within divisions", an mdiv element may contain additional mdiv sub-elements nested to any level required. For example, the encoding of a multi-movement work, such as a symphony, might have the following structure:

<body>
<mdiv type="symphony">
<mdiv n="1" type="movement">
<!-- contents of mvt 1 -->
</mdiv>
<mdiv n="2" type="movement">
<!-- contents of mvt 2 -->
</mdiv>
<mdiv n="3" type="movement">
<!-- contents of mvt 3 -->
</mdiv>
<mdiv n="4" type="movement">
<!-- contents of mvt 4 -->
</mdiv>
</mdiv>
</body>
Listing 11.

While dramatic works, such as Verdi's opera, Il Trovatore, often exhibit a more deeply-nested structure:

<body>
<mdiv type="opera">
<mdiv n="I" type="act">
<mdiv n="1" type="scene">
<!-- contents of act I, sc. 1 -->
</mdiv>
<mdiv n="2" type="scene">
<!-- contents of act I, sc. 2-->
</mdiv>
<mdiv n="3" type="scene">
<!-- contents of act I, sc. 3 -->
</mdiv>
</mdiv>
<mdiv n="II" type="act">
<mdiv n="1" type="scene">
<!-- contents of act II, sc. 1 -->
</mdiv>
<mdiv n="2" type="scene">
<!-- contents of act II, sc. 2 -->
</mdiv>
<mdiv n="3" type="scene">
<!-- contents of act II, sc. 3 -->
</mdiv>
<mdiv n="4" type="scene">
<!-- contents of act II, sc. 4 -->
</mdiv>
<mdiv n="5" type="scene">
<!-- contents of act II, sc. 5 -->
</mdiv>
</mdiv>
<mdiv n="III" type="act">
<mdiv n="1" type="scene">
<!-- contents of act III, sc. 1 -->
</mdiv>
<mdiv n="2" type="scene">
<!-- contents of act III, sc. 2 -->
</mdiv>
<mdiv n="3" type="scene">
<!-- contents of act III, sc. 3 -->
</mdiv>
</mdiv>
<mdiv n="IV" type="act">
<mdiv n="1" type="scene">
<!-- contents of act IV, sc. 1 -->
</mdiv>
<mdiv n="2" type="scene">
<!-- contents of act IV, sc. 2 -->
</mdiv>
<mdiv n="3" type="scene">
<!-- contents of act IV, sc. 3 -->
</mdiv>
</mdiv>
</mdiv>
</body>
Listing 12.

Conventionally, in performance the musical structures represented by mdiv elements are separated by pauses; however, attacca, attacca subito, seque, or similar terms are sometimes used at the end of an mdiv to indicate that the next mdiv should begin immediately after the conclusion of the current one. These terms have no effect, however, on the logical segmentation of musical content using mdiv elements.

2.1.2.2Content of Musical Divisions

The contents of mdiv can be organised according to the two encoding paradigms provided by the score and parts elements.

Full score view of the musical content.
Provides a container for performers' parts.

The score element represents notation in which all the parts of an ensemble are arranged on vertically aligned staves, while the parts element collects the individually notated parts for each performer or group of performers. The explicit encoding of these two ‘views’ is necessary because it is not always possible or desirable to automatically derive one view from the other. In addition, separating scores and parts can eliminate a great deal of markup complexity.

<body>
<mdiv n="1" type="movement">
<score>
<!-- markup of score goes here -->
</score>
<parts>
<!-- markup of performers’ parts goes here -->
</parts>
</mdiv>
<!-- additional movements go here -->
</body>
Listing 13.

The score and parts elements may also be employed to accommodate different methods of organizing the markup – with no particular presentation implied. In this case, software may render a collection of parts as a score or a score as a collection of parts.

Within the collective parts element, notation for a single performer is represented by the part element:

An alternative visual rendition of the score from the point of view of a particular performer (or group of performers).

A part is effectively a small-scale score, allowing all the encoding features of a full score, such as multiple staves, performance directives, and so on. A group of part elements is useful for encoding performing parts when there is no score, such as in early music part books; when the parts have non-aligning bar lines; when different layout features, such as page turns, are needed for the score and parts; or for accommodating software that requires part-by-part encoding.

Please note that part elements in MEI are not an indication of voice leading or staff grouping. Voice leading can be encoded using the next attribute, available on all the members of the model.eventLike class. The staffGrp element handles grouping of staves in the score context.

<parts>
<part label="Violin 1">
<!-- first performer’s part -->
</part>
<part label="Violin 2">
<!-- second performer’s part -->
</part>
<!-- additional performers’ parts -->
</parts>
Listing 14.

In both score and part views, the scoreDef element is used to describe logical characteristics of the encoded music, such as key signature, the sounding key (as opposed to the notated key signature), meter, etc., and visual features, such as page size, staff groupings and display labels, etc. The staffGrp elements within scoreDef and the order of staffDef elements inside staffGrp should follow the score order of the source for the encoding.

A part or score may be further divided into linear segments called "sections".

Segment of music data.

section elements are often used as a scoping mechanism for clef signs, key and meter signatures, as well as metronome, tempo, and expression markings. Using section elements can help to minimize the need for backward scanning to establish context when the starting point for access is not at the beginning of the score. section elements may also be used for other user-defined, i.e., analytical or editorial, purposes and may therefore be arbitrarily nested to any desired level.

The ending element shares the same model as the section element. Unlike section, however, it may not be recursively nested.

Alternative ending for a repeated passage of music; i.e., prima volta, seconda volta, etc.

The most common (non-analytical, non-editorial) use of section and ending elements is illustrated below:

<music>
<body>
<mdiv>
<score>
<section>
<!-- section one to be repeated -->
</section>
<ending n="1">
<!-- 1st ending -->
</ending>
<ending n="2">
<!-- 2nd ending -->
</ending>
<section>
<!-- next section -->
</section>
</score>
</mdiv>
</body>
</music>
Listing 15.

Within section elements, several methods of organization are possible, depending upon the notational style of the source material and the encoder's needs. For example, when the MEI.cmn module is used, the default organization is measure-by-measure, with staff and layer sub-elements within each measure. Further discussion of CMN notation is continued in chapter 4 Repertoire: Common Music Notation.

However, staff-by-staff organization is more appropriate for music without measures and is provided when either the MEI.mensural or MEI.neumes module is employed. Coverage of mensural notation is provided in chapter 5 Repertoire: Mensural Notation, while 6 Repertoire: Neume Notation describes neumatic notation.

It must be noted that, when both the MEI.cmn and MEI.mensural modules are available, it is possible to encode CMN notation without using measure elements; that is, staff-by-staff organization may be used and the ends of measures marked using barLine elements.

In certain circumstances, this approach may be preferable for reproduction of the visual layout of the music. However, the simultaneous use of the measure and barLine elements may lead to confusion and should be avoided.

Typically, MEI follows the order of sections as they appear in the document being encoded. When performance requires a different order, for instance in the case of D.C. and D.S. directives, the following element may be used to define the performance order.

Indicates how a section may be programmatically expanded into its 'through-composed' form.

In the following example, expansion is used to indicate how the notated sections should be ordered in a "through-composed" rendition, for example for machine performance or analysis. The plist attribute contains an ordered list of identifiers of descendant section, ending, lem, or rdg elements. The sequence of values in the plist attribute indicates that the section labelled 'A' comes first, then the section labelled 'B', followed by the 'A' section again. This mechanism must be specified independently of any textual directives, such as "Da capo" or "D.S. al Fine", that may be present in the document.

<music>
<body>
<mdiv>
<score>
<section>
<expansion plist="#shared.A #shared.B #shared.A"/>
<section xml:id="shared.A">
<!-- "A" section -->
</section>
<section xml:id="shared.B">
<!-- "B" section -->
</section>
</section>
</score>
</mdiv>
</body>
</music>
Listing 16.

2.1.3Document Layout Elements

This section introduces the elements that can be used to represent document layout features in MEI, be it for the sake of capturing an original source's layout when transcribing or setting up layout features in so called ‘born digital’ documents.

(page beginning) – An empty formatting element that forces text to begin on a new page.
@
Provides a number-like designation that indicates an element's position in a sequence of similar elements. May not contain space characters.

The pb element can be used to mark page beginnings. When transcribing an existing document the n attribute should be used to record the page number displayed in the source. It need not be an integer, e.g., 'iv', or 'p17-3'. The logical page number can be calculated by counting previous pb ancestor elements. When used in a score context, a page beginning implies an accompanying system beginning. This element is modelled on an element in the Text Encoding Initiative (TEI) standard.

(page description) – Contains a brief prose description of the appearance or description of the content of a physical page.

Additional information can be provided on page beginnings. Ranging from a prose description of the page layout in pgDesc to defined headers and footers.

(page header) – A running header on the first page. Also, used to temporarily override a running header on individual pages.
(page header 2) – A running header on the pages following the first.
(page footer) – A running footer on the first page. Also, used to temporarily override a running footer on individual pages.
(page footer 2) – A running footer on the pages following the first.

Columned layout can be captured with the following elements:

(column beginning) – An empty formatting element that forces text to begin in a new column.
@
n (cb)
Records the column number.
(column layout) – An empty formatting element that signals the start of columnar layout.

In order to force a system break in the musical text sb can be used.

(system beginning) – An empty formatting element that forces musical notation to begin on a new line.

Critical editions and collections of works often contain extensive text, such as a title page, table of contents, an introductory essay, commentary, biographical sketch, index, etc. These textual items may appear in either the front or back elements. The front and back elements, available only when the MEI.text module is activated, are described more fully in chapter 9.2 Text in MEI.

(front matter) – Bundles prefatory text found before the start of the musical text.
(back matter) – Contains any appendixes, advertisements, indexes, etc. following the main body of a musical text.

2.1.4General Text Structure Elements

The MEI.shared module provides basic text structure elements.

(division) – Major structural division of text, such as a preface, chapter or section.
(heading) – Contains any heading, for example, the title of a section of text, or the heading of a list.
(line group) – May be used for any section of text that is organized as a group of lines; however, it is most often used for a group of verse lines functioning as a formal unit, e.g. a stanza, refrain, verse paragraph, etc.
(line beginning) – An empty formatting element that forces text to begin on a new line.
(paragraph) – One or more text phrases that form a logical prose passage.

A detailed description of their use and of other elements from the MEI.text module can be found in the corresponding chapter 9.2 Text in MEI.

2.2General Music Elements

This section lists the elements defined in the shared module that are available within the music element.

2.2.1Score and Parts

The following elements are provided for the capture of scores and parts:

Full score view of the musical content.
Provides a container for performers' parts.
An alternative visual rendition of the score from the point of view of a particular performer (or group of performers).
(score definition) – Container for score meta-information.
(staff definition) – Container for staff meta-information.
(layer definition) – Container for layer meta-information.
(staff group) – A group of bracketed or braced staves.
(group symbol) – A brace or bracket used to group two or more staves of a score or part.
A container for document text that identifies the feature to which it is attached. For a "tool tip" or other generated label, use the attribute.
Indication of the exact location of a particular note on the staff and, therefore, the other notes as well.
(clef group) – A set of simultaneously-occurring clefs.
(key signature) – Written key signature.
(key accidental) – Accidental in a key signature.

The character of elements specifying one or more score or staff parameters, such as meter and key signature, clefs, etc., is that of a milestone; that is, they affect all subsequent material until a following redefinition. A scoreDef element, which may affect more than just one staff, is allowed only within score, part and section elements, whereas staffDef is allowed only within staffGrp, staff and layer. A staffDef nested inside a staff must bear the same value for its n attribute as its parent staff and may thus not affect other staves.

The actual use of these elements depends on the repertoire and historical context of the source material. For details on their use in Common Western Notation, please refer to chapter 4.2.2 Defining Score Parameters for CMN.

2.2.2Staves and Layers

The elements below are used to capture the logical organization of musical notation:

A group of equidistant horizontal lines on which notes are placed in order to represent pitch or a grouping element for individual 'strands' of notes, rests, etc. that may or may not actually be rendered on staff lines; that is, both diastematic and non-diastematic signs.
An independent stream of events on a staff.

The actual use of the staff and layer elements depends on the repertoire and historical context of the source material. For details on their use in Common Western Notation, please refer to chapter 4 Repertoire: Common Music Notation. For mensural notation, see chapter 5 Repertoire: Mensural Notation, and for neumatic notation, chapter 6 Repertoire: Neume Notation.

2.2.3Basic Music Events

The basic features of music notation are represented by the following elements:

A single pitched event.
A simultaneous sounding of two or more notes in the same layer *with the same duration*.
A non-sounding event found in the source being transcribed.

The characteristics of stems on notes and chords are indicated by means of attributes found in the att.stems class.

@
stem.dir (att.stems)
Describes the direction of a stem.
@
stem.len (att.stems)
Encodes the stem length.
@
stem.mod (att.stems)
Encodes any stem "modifiers"; that is, symbols rendered on the stem, such as tremolo or Sprechstimme indicators.
@
stem.pos (att.stems)
Records the position of the stem in relation to the note head(s).
@
stem.x (att.stems)
Records the output x coordinate of the stem's attachment point.
@
stem.y (att.stems)
Records the output y coordinate of the stem's attachment point.

2.2.4Other events

Because they can occur in the context of a stream of events on the staff, some elements which are used in other contexts are also treated as events. For example, in addition to being used to define the initial clef of a staff, the clef element can also be used to indicate a clef change.

2.2.4.1Key Signatures and Clefs

Key signatures and clefs as well as intra-staff changes to these musical parameters are treated as events.

(key signature) – Written key signature.
(key accidental) – Accidental in a key signature.
Indication of the exact location of a particular note on the staff and, therefore, the other notes as well.
(clef group) – A set of simultaneously-occurring clefs.

2.2.4.2Bar Lines and Custos Signs

Measure separators, i.e., bar lines, and custos signs are also considered to be events.

Vertical line drawn through one or more staves that divides musical notation into metrical units.
Symbol placed at the end of a line of music to indicate the first note of the next line. Sometimes called a "direct".

2.2.4.3Accidentals, Articulation Symbols, Augmentation Dots, and Custos Signs

The following elements are regarded as events primarily because they sometimes occur independently of any associated notes, rests, or chords, especially in mensural and neume repertoires.

(accidental) – Records a temporary alteration to the pitch of a note.
(articulation) – An indication of how to play a note or chord.
Dot of augmentation or division.

<mei meiversion="4.0.0">
<meiHead meiversion="4.0.0">
<fileDesc>
<titleStmt>
<title>Alignment of editorial accidentals</title>
</titleStmt>
<pubStmt>
<date>2017-05-17</date>
</pubStmt>
<notesStmt>
<annot>Editorial accidentals are aligned on the centre of the notehead.</annot>
</notesStmt>
</fileDesc>
<encodingDesc>
<appInfo>
<application version="0.9.13">
<name>Verovio</name>
</application>
</appInfo>
</encodingDesc>
<workDesc>
<work>
<titleStmt>
<title/>
</titleStmt>
</work>
</workDesc>
</meiHead>
<music meiversion="4.0.0">
<body>
<mdiv xml:id="mdiv-0000001056540324">
<score xml:id="score-0000000884943276">
<scoreDef xml:id="scoredef-000000027977328" n="1" label="feature-example">
<staffGrp xml:id="m-000000028778056">
<staffDef xml:id="staffdef-000000129725177" n="1" lines="5" clef.shape="G" clef.line="2"/>
</staffGrp>
</scoreDef>
<section xml:id="section-000000076944697">
<measure xml:id="measure-L2" right="end" n="1">
<staff xml:id="staff-L2F1" n="1">
<layer xml:id="layer-L2F1" n="1">
<note xml:id="note-L3F1" dur="1" oct="5" pname="f">
<accid xml:id="accid-000000113038940" accid="s" func="edit"/>
</note>
<note xml:id="note-L4F1" dur="1" oct="5" pname="f">
<accid xml:id="accid-000000162539045" accid="f" func="edit"/>
</note>
<note xml:id="note-L5F1" dur="1" oct="5" pname="f">
<accid xml:id="accid-000000208946960" accid="n" func="edit"/>
</note>
<note xml:id="note-L6F1" dur="1" oct="5" pname="f">
<accid xml:id="accid-000000207644959" accid="x" func="edit"/>
</note>
<note xml:id="note-L7F1" dur="1" oct="5" pname="f">
<accid xml:id="accid-000000179518178" accid="ff" func="edit"/>
</note>
</layer>
</staff>
</measure>
</section>
</score>
</mdiv>
</body>
</music>
</mei>
Listing 17.

2.2.4.4Lyric Syllables

The syl element is used to mark a word or portion of a word that is to be vocally performed. A fuller description of its use is provided in chapter 8.2 Lyric Syllables.

(syllable) – Individual lyric syllable.

2.2.4.5Event Spacing

The following elements provide control over the horizontal spacing of notational events, such as notes, chords, rests, etc.:

A placeholder used to fill an incomplete measure, layer, etc. most often so that the combined duration of the events equals the number of beats in the measure.

In this context, the term ‘space’ is used to mean whitespace that is required to meaningfully align multiple voices in a multi-voice texture. In DARMS these were referred to as ‘push codes’. The space element is most often used when a new voice appears on a staff mid-measure.

The space element may also be used to align material that crosses staves.

‘Space’ can be thought of as another kind of event. In fact, some refer to this concept as an ‘invisible rest’.

While ‘space’ is meaningful, ‘padding’ is non-essential whitespace that is used to shift the position of the events which follow.

(padding) – An indication of extra visual space between notational elements.

The pad element is provided in order to capture software-dependent placement information when it is desirable to do so. Unless the MEI file will be used as an intermediate file format, this is usually not necessary.

2.2.5Expression Marks

Expression marks are instructions in the form of words, abbreviations, or symbols that convey aspects of performance that cannot be expressed purely through the musical notation.

2.2.5.1Text Directives

All of the following elements can be considered text directives; however, MEI uses the dir element specifically for words, abbreviations, numbers, or symbols specifying or suggesting the manner of performance that are not encoded elsewhere using the more specific elements of tempo and dynam.

(directive) – An instruction expressed as a combination of text and symbols — such as segno and coda symbols, fermatas over a bar line, etc., typically above, below, or between staves, but not on the staff — that is not encoded elsewhere in more specific elements, like or .

Examples of directives include text strings such as 'affettuoso', fingering numbers, or music symbols such as segno and coda symbols or fermatas over a bar line. Directives can be control elements. That is, they can linked via their attributes to other events. The starting point of the directive may be indicated by either a tstamp, tstamp.ges, tstamp.real or startid attribute, while the ending point may be recorded by either a tstamp2, dur, dur.ges or endid attribute. It is a semantic error not to specify a starting point attribute.

2.2.5.2Tempo

Tempo marks are indications through words, abbreviations, or specific metronome settings of the speed at which a piece of music is to be performed. Both instantaneous and continuous tempo markings may be encoded using this element.

Text and symbols descriptive of tempo, mood, or style, e.g., "allarg.", "a tempo", "cantabile", "Moderato", "♩=60", "Moderato ♩ =60").

<mei meiversion="4.0.0">
<meiHead meiversion="4.0.0">
<fileDesc>
<titleStmt>
<title>Tempo example</title>
</titleStmt>
<pubStmt>
<date>2019-10-25</date>
</pubStmt>
<notesStmt>
<annot>Verovio supports "tempo" elements. Horizontal positioning can be specified. By default, tempi indications are placed above the staff. The "rend" element can used within the text, for example for specifying metronome values.</annot>
</notesStmt>
</fileDesc>
<encodingDesc>
<appInfo>
<application version="0.9.13">
<name>Verovio</name>
</application>
</appInfo>
</encodingDesc>
</meiHead>
<music meiversion="4.0.0">
<body>
<mdiv>
<score>
<scoreDef meter.sym="cut">
<staffGrp>
<staffDef n="1" label="Violino" lines="5" clef.line="2" clef.shape="G"/>
</staffGrp>
</scoreDef>
<section>
<measure n="0" type="upbeat">
<staff n="1">
<layer n="1">
<beam>
<note xml:id="m0_s2_e1" pname="e" oct="5" dur="8"/>
<note xml:id="m0_s2_e2" pname="f" oct="5" dur="8"/>
</beam>
</layer>
</staff>
<tempo tstamp="1" staff="1">Andante con moto
<rend fontname="VerovioText"></rend>
= 70 </tempo>
<slur startid="#m0_s2_e1" endid="#m0_s2_e2"/>
</measure>
<measure n="1">
<staff n="1">
<layer n="1">
<note xml:id="m1_s2_e1" pname="g" oct="5" dur="4" dots="1"/>
<note xml:id="m1_s2_e2" pname="g" oct="5" dur="8"/>
<note xml:id="m1_s2_e3" pname="g" oct="5" dur="4"/>
<beam>
<note xml:id="m1_s2_e4" pname="g" oct="5" dur="8"/>
<note xml:id="m1_s2_e5" pname="c" oct="6" dur="8"/>
</beam>
</layer>
</staff>
<slur startid="#m1_s2_e4" endid="#m1_s2_e5"/>
</measure>
</section>
</score>
</mdiv>
</body>
</music>
</mei>
Listing 18.

2.2.5.3Dynamics

Dynamics, or dynamic marks, are terms, abbreviations, and symbols that indicate the specific degrees of volume of a note, phrase, or section of music, e.g., "piano", "forte". Transitions from one volume level to another, e.g., "crescendo", "diminuendo", are also specified through dynamic marks.

(dynamic) – Indication of the volume of a note, phrase, or section of music.

2.2.5.4Phrase Marks

Phrase marks are curved lines placed over or under notes to delineate short sections of a work that represent a unified melodic idea, analogous to a phrase in literature.

Indication of 1) a "unified melodic idea" or 2) performance technique.
Indication of 1) a "unified melodic idea" or 2) performance technique.

MEI maintains a distinction between phrase marks and slurs, the latter being curved lines over or under a sequence of notes indicating they are to be performed using a particular playing/singing technique, notes that should be taken in a single breath by wind instruments or played by string instruments using a single stroke of the bow. Often, a slur also indicates that the affected notes should be played in a legato manner.

Even so, it is common for both of these concepts to be referred to generically as "slurs". Therefore, unless one is encoding music from a repertoire in which this distinction is important, the slur element should be preferred over phrase.

2.2.5.5Ornaments

Ornaments are formulae of embellishment that can be realized by adding supplementary notes to one or more notes of the melody.

An element indicating an ornament that is not a mordent, turn, or trill.

MEI provides a generic element for encoding an ornament symbol that is not a mordent, turn, or trill. For those common CMN ornaments, please refer to 4.4 Common Music Notation Ornaments.

Ornaments can be represented as textual strings (e.g. with a Unicode symbol) or with a user defined symbol (for the latter also see 2.4 User-defined Symbols).

Ornamentsmay also be encoded as so called control events (see also: 1.2.2 Events and Controlevents). That is, they be can linked via their attributes to other events. It is a semantic error not to specify a starting point attribute with either tstamp or startid.

2.3Common Attributes

The following attributes, all of which are defined in separate attribute classes but are also provided through the att.common attribute class, are available on nearly all elements in an MEI encoding. They provide e.g. the means to identify, label, or reference elements in MEI-encoded files.

2.3.1Attributes from the XML-namespace

The most general attributes that are very frequently encountered in MEI files are not even native MEI attributes but are coming from the basic definition of XML in the XML-namespace http://www.w3.org/XML/1998/namespace. MEI redefines some of them in the att.basic class.

@
xml:id (att.id)
Regularizes the naming of an element and thus facilitates building links between it and other resources. Each id attribute within a document must have a unique value.

The value of the xml:id attribute serves as an identifier for an element and its content. Its value must be unique in the context of the current document and must conform to the definition of an XML Name provided by the W3C Recommendation at http://www.w3.org/TR/xml/#NT-Name. Suggestions for constructing an xml:id value can be found at http://www.w3.org/TR/xml/#sec-suggested-names.

The xml:id attribute may take values similar to the following:

<!-- The following are all valid IDs. -->
<note xml:id="n1"/>
<note xml:id="_n1"/>
<note xml:id="thisIsMyFavoriteNote"/>
<note xml:id="shared.thisIsMyFavoriteNote"/>
Listing 19.

This is an example of an incorrectly-formulated xml:id value:

<!-- xml:id not valid as IDs are not allowed to start with a number. -->
<note xml:id="1"/>
Listing 20.

@
xml:base (att.basic)
Provides a base URI reference with which applications can resolve relative URI references into absolute URI references.

At many locations in an MEI file one can reference internal or external references. E.g. the following example defines a graphic and references an external image (entity) by means of the target attribute:

<graphic target="myImage.jpg"/>
Listing 21.

When a reference to an external entity is not a complete URI it is resolved against the current base URI; if not defined by other means this would be the location of the current document. The above example consequently would mean, that the file `myImage.jpg` referenced from graphic resides at the same location (in the same folder) as the MEI-file.

The xml:base attribute may be used “to specify a base URI other than the base URI of the document or external entity.” (Marsch, Jonathan; Tobin, Richard: XML Base (Second Edition). W3C Recommendation 28 January 2009. online at: http://www.w3.org/TR/2009/REC-xmlbase-20090128/).

<graphic target="myImage.jpg" xml:base="http://www.mySite.org/images/"/>
Listing 22.

The value of xml:base can be inherited from an ancestor. This is relevant for resolving relative links or URIs within the document. A comprehensible use case can be illustrated by the following example: the values of the graphic elements' target attribute can be completed by the xml:base value specified for the ancestor facsimile element:

<facsimile xml:base="http://www.mySite.org/images/">
<surface>
<graphic target="myImage.jpg"/>
<graphic target="myImage.tif"/>
</surface>
</facsimile>
Listing 23.

In order to determine an absolute URI, the base URIs of the element and all its ancestors (including the document node) have to be taken into account. In the above case the relative URIs of graphic/@target would consequently resolve to:

``` http://www.mySite.org/images/myImage.jpg http://www.mySite.org/images/myImage.tif ```

For more information on xml:base see: https://www.w3.org/TR/xmlbase/

The xml:id and xml:base attributes are especially important when it comes to linking document fragments to eachother or to external entities. Many of the linking attributes are globally available in MEI through the att.common attribute class.

Yet there are other attributes from the XML-Namespace encountered in MEI files.

@
xml:lang (att.lang)
Identifies the language of the element's content. The values for this attribute are language 'tags' as defined in BCP 47. All language tags that make use of private use sub-tags must be documented in a corresponding language element in the MEI header whose id attribute is the same as the language tag's value.
@
xml:space (att.whitespace)
Allows one to signal to an application whether an element's white space is "significant". The behavior of xml:space cascades to all descendant elements, but it can be turned off locally by setting the xml:space attribute to the value "default".

While xml:lang attribute may be used to encode the language of an element's contents, the xml:space attribute lets you define the handling of whitespace, i.e. whitespace being important content (xml:space="preserve") of negligible (xml:space="default"). With the latter also being the default value if no xml:space attribute is present.

2.3.2Label Attributes

@
label (att.labelled)
Captures text to be used to generate a label for the element to which it's attached, a "tool tip" or prefatory text, for example. Should not be used to record document content.
@
Provides a number-like designation that indicates an element's position in a sequence of similar elements. May not contain space characters.
@
Provides a numeric designation that indicates an element's position in a sequence of similar elements. Its value must be a non-negative integer.

The label and n attributes both serve a labeling function; however, they differ in the values they allow. The n attribute must be a single token, while label may contain a string value that includes spaces. This makes label useful for the capture of free-text labels, but a name or number specified with n may be easier to process.

<!-- Example of a @label containing whitespace: -->
<mdiv label="Allegro moderato">
<!-- … -->
</mdiv>
<!-- Example of a processable @n attribute: -->
<measure n="42">
<!-- … -->
</measure>
Listing 24.

2.3.3Classification Attributes

@
class (att.classed)
Contains one or more URIs which denote classification terms that apply to the entity bearing this attribute.
@
type (att.typed)
Designation which characterizes the element in some sense, using any convenient classification scheme or typology that employs single-token labels.

2.3.4Responsibility Attributes

@
Indicates the agent(s) responsible for some aspect of the text's transcription, editing, or encoding. Its value must point to one or more identifiers declared in the document header.

2.3.5Linking Attributes

@
copyof (att.linking)
Points to an element of which the current element is a copy.
@
corresp (att.linking)
Used to point to other elements that correspond to this one in a generic fashion.
@
follows (att.linking)
points to one or more events in a user-defined collection that are known to be predecessors of the current element.
@
next (att.linking)
Used to point to the next event(s) in a user-defined collection.
@
precedes (att.linking)
Points to one or more events in a user-defined collection that are known to be successors of the current element.
@
prev (att.linking)
Points to the previous event(s) in a user-defined collection.
@
sameas (att.linking)
Points to an element that is the same as the current element but is not a literal copy of the current element.
@
synch (att.linking)
Points to elements that are synchronous with the current element.

For a detailed description of linking mechanisms used in MEI also see the section on 13 Linking Data.

2.4User-defined Symbols

This chapter describes the elements, model classes, and attribute classes that are part of the MEI.usersymbols module.

2.4.1Overview of the Usersymbols Module

The module described in this chapter makes available the following components:

2.4.1.1Elements

Container for text that is fixed to a particular page location, regardless of changes made to the layout of the measures around it.
A curved line that cannot be represented by a more specific element, such as a slur.
A visual line that cannot be represented by a more specific; i.e., semantic, element.
A reference to a previously defined symbol.
(symbol definition) – Declaration of an individual symbol in a symbolTable.
Contains a set of user-defined symbols.

2.4.1.2Attribute Classes

No attribute classes are defined in this module.

2.4.1.3Model Classes

The usersymbols module defines the following model classes:

model.graphicPrimitiveLike model.symbolTableLike

2.4.2Uses of the Usersymbols Module

The elements provided by the usersymbols module may be used in two ways:

  • For defining lines, curves and text elements that cannot be represented by a more specific element.
  • For defining reusable symbols and special graphical renditions.

For this purpose, it provides three elements as graphic primitives, line, curve and anchoredText. Anywhere these elements are allowed, the symbol element can be used as well. The symbol element facilitates the re-use of symbols that were defined by symbolDef elements.

2.4.2.1Defining Reusable Symbols

The symbolDef element uses SVG markup or the aforementioned graphic primitives to describe a symbol. A symbol definition may also use symbols defined by other symbolDef elements by employing the symbol element.

The following code snippet shows a definition of a triangle percussion symbol using graphic primitives:

<symbolDef xml:id="userSymbols.triangleSymbol3">
<line x="0" x2="2.55" y="0" y2="4.25"/>
<line x="2.55" x2="5.1" y="4.25" y2="0"/>
<line x="5.1" x2="0.85" y="0" y2="0"/>
</symbolDef>
Listing 25. Definition of a triangle percussion symbol using graphic primitives
Figure 1. Rendition of the triangle defined above

The following snippet encodes a symbol composed of the symbol defined above and additional graphics primitives:

<symbolDef xml:id="userSymbols.triangleSymbolWithStick">
<symbol ref="#userSymbols.triangleSymbol3"/>
<line x="2.55" x2="5.95" y="1.25" y2="3.4"/>
</symbolDef>
Listing 26. Symbol composed of the symbol defined above and additional graphics primitives
Figure 2. Rendition of the composite triangle symbol

2.4.2.2Elements Without Semantic Implications

The graphics primitives and symbols can be used directly in the music to describe text and lines on a purely graphical level, without implying a specific logical meaning. If possible, however, more meaningful elements should be used. This means for example, "a tempo" or "da capo" should in general not be put inside anchoredText. Instead, tempo and dir should be used. Likewise, slurs and ties should be encoded using their respective elements, not using curve, and for glissandi, gliss should be used instead of line.

An example usage for line is the visualization of voice leading, which is not covered by a specific MEI element.

Figure 3. Voice leading visualization as found in an Edition Peters print of Album für die Jugend by Schumann, No. 35 (Mignon), measure 6. (Unknown date, plate number is 10478.)

The following code snippet shows the encoding of the above example:

<measure n="6">
<staff n="1">
<layer n="1">
<rest dur="4" xml:id="userSymbols.r1"/>
<beam>
<note dur="8" oct="4" pname="c" xml:id="userSymbols.n1"/>
<note dur="8" oct="4" pname="e" xml:id="userSymbols.n2"/>
</beam>
<beam>
<note dur="8" oct="4" pname="g" xml:id="userSymbols.n3"/>
<note dur="8" oct="4" pname="e" xml:id="userSymbols.n4"/>
<note dur="8" oct="4" pname="b" xml:id="userSymbols.n5"/>
<note dur="8" oct="4" pname="g" xml:id="userSymbols.n6"/>
</beam>
<slur curvedir="above" endid="#userSymbols.n6" startid="#userSymbols.n1"/>
</layer>
<layer n="2">
<rest dur="4"/>
<note dur="2" next="#userSymbols.n9" oct="4" pname="c" stem.dir="down" xml:id="userSymbols.n7"/>
</layer>
</staff>
<staff n="2">
<layer n="1">
<note dots="1" dur="2" oct="2" pname="g" xml:id="userSymbols.n8"/>
<note dur="4" oct="3" pname="b" prev="#userSymbols.n7 #userSymbols.n8" xml:id="userSymbols.n9"/>
<slur curvedir="above" endid="#userSymbols.n9" startid="#userSymbols.n8"/>
</layer>
</staff>
<line endid="#userSymbols.n9" rend="dotted" startid="#userSymbols.n7"/>
</measure>
Listing 27. Encoding of the Schumann example

2.4.2.3Defining a Specific Graphical Rendition for a Semantic Element

Usersymbols can define the rendition of different elements in two ways. Some elements, for example dir and tempo, can have user symbol elements as content. In the following example, the content of dir is used to provide pictograms of percussion instruments.

Figure 4. Indicating percussion instruments using pictograms

The corresponding encoding would be as follows:

<section>
<scoreDef meter.count="4" meter.unit="4">
<symbolTable>
<symbolDef xml:id="userSymbols.triangleSymbol1">
<line x="0" x2="2.55" y="0" y2="4.25"/>
<line x="2.55" x2="5.1" y="4.25" y2="0"/>
<line x="5.1" x2="0.85" y="0" y2="0"/>
<line x="2.55" x2="5.95" y="1.25" y2="3.4"/>
</symbolDef>
<symbolDef xml:id="userSymbols.cowbellSymbol">
<line x="1" x2="1.8" y="0" y2="4"/>
<line x="1.8" x2="4.2" y="4" y2="4"/>
<line x="4.2" x2="5" y="4" y2="0"/>
<line x="5" x2="1" y="0" y2="0"/>
<curve bezier="0 1.5 0 1.5" endho="3" endvo="4" startho="1" startvo="4"/>
</symbolDef>
</symbolTable>
<staffGrp>
<staffDef clef.line="2" clef.shape="G" n="1"/>
</staffGrp>
</scoreDef>
<measure n="1">
<staffDef n="1">
<instrDef midi.instrname="Open_Triangle"/>
</staffDef>
<staff n="1">
<layer>
<dir tstamp="1">
<symbol ref="#userSymbols.triangleSymbol2"/>
</dir>
<note dur="1"/>
</layer>
</staff>
</measure>
<measure n="2">
<staffDef n="1">
<instrDef midi.instrname="Cowbell"/>
</staffDef>
<staff n="1">
<layer>
<dir tstamp="1">
<symbol ref="#userSymbols.cowbellSymbol"/>
</dir>
<note dur="4"/>
<note dur="4"/>
<note dur="4"/>
<note dur="4"/>
</layer>
</staff>
</measure>
</section>
Listing 28. Encoding of above example

A number of elements can point to an internally-defined symbol for rendering using the altsym attribute.

Figure 5. Different treble clef renditions as written by Charpentier (source: Journal of Seventeenth-Century Music, Volume 12, No. 1 (2006), figure 3) http://www.sscm-jscm.org/v12/no1/gosine.html

<scoreDef>
<symbolTable>
<symbolDef xml:id="userSymbols.clefA">
<curve bezier="-1.2 0.1 -0.9 -0.8" endho="1.1" endvo="6.6" startho="1.2" startvo="4"/>
<curve bezier="1 0.9 0.1 1.6" endho="3" endvo="5.3" startho="1.1" startvo="6.6"/>
<curve bezier="-0.1 -2.6 0 2.3" endho="0.6" endvo="-0.1" startho="3" startvo=" 5.3"/>
<curve bezier="0.07 -1.3 -0.2 -1.63" endho="2.4" endvo="0.23" startho="0.6" startvo="-0.1"/>
<curve bezier="0.2 1.3 0.5 0.62" endho="0.8" endvo="0.81" startho="2.4" startvo="0.23"/>
</symbolDef>
<symbolDef xml:id="userSymbols.clefB">
<curve bezier="-0.7 0.1 0.3 0.92" endho="0.7" endvo="-0.2" startho="2.5" startvo=" 1.3 "/>
<curve bezier="-0.27 -0.76 -1.25 -1.26" endho="2" endvo="-0.74" startho="0.7" startvo="-0.2"/>
<curve bezier="1.4 1.8 0.4 -1" endho="1.6" endvo="4.36" startho="2" startvo="-0.74"/>
<curve bezier="-0.89 2.2 -1.1 1.6" endho="3.5" endvo="6.06" startho="1.6" startvo="4.36"/>
<curve bezier="0.8 -1.2 0 0" endho="3.7" endvo="2.66" startho="3.5" startvo="6.06"/>
</symbolDef>
</symbolTable>
<staffGrp>
<staffDef n="1">
<clef altsym="#userSymbols.clefA" line="2" shape="G"/>
</staffDef>
<staffDef n="2">
<clef altsym="#userSymbols.clefB" line="2" shape="G"/>
</staffDef>
</staffGrp>
</scoreDef>
Listing 29. Defining two staffs, each using its own treble clef shape

Externally-defined symbols may be referenced using a glyph.name or glyph.num attribute from the att.extSym attribute class. Both attributes refer to Standard Music Font Layout (SMuFL) characters, if not specified differently by the glyph.auth and glyph.uri attributes.

<ornam tstamp="1">
<symbol glyph.auth="smufl" glyph.num="#xE5C0" glyph.name="ornamentPrecompDoubleCadenceLowerPrefix"/>
</ornam>
Listing 30. Use of glyph.auth and glyph.name and glyph.num attributes to refer to a SMUFL symbol

<meterSig count="2" form="norm" glyphname="timeSigCutCommon" glyphnum="U+E08B" sym="cut" unit="4"/>
Listing 31. Use of glyphname and glyphnum attributes

2.4.3Positioning and Coordinates

2.4.3.1Axis Orientation

MEI uses the classic axis directions where the x-axis points from left to right and the y-axis points from bottom up. (This is compatible with PostScript's axis orientation, while SVG's y-axis points in the opposite direction.)

2.4.3.2Units

There are two types of units used by MEI: Staff units and units of the output coordinate system. Units of the output coordinate system can be translated to physical real world distances by means of the vu.height and page.scale of a scoreDef element. Real world units are multiplied by the value of page.scale to get the corresponding value in output coordinate units.

If an element is scaled using the scale attribute, the actual size of the units changes accordingly.

2.4.3.3Positioning

An element may be positioned using either absolute or relative coordinates. If absolute start point coordinates are specified using x/y coordinates (or their relatives x2/y2 for endpoints) they take precedence over relative positions specified by ho/vo/to (or startho/startvo/startto). Analogously, x2/y2 override endho/endvo/endto.

If to/startto/endto attributes are used, the start or end point is x-aligned with the indicated timestamp.

If relative start coordinates (ho/vo or startho/startvo) are used, the origin of the coordinate system to be used for the start point is the first one found by the following search schema:

  • If startid is present, the origin of the referenced element;
  • If the element is inside running text (e.g. inside tempo), the end of the preceding text or element;
  • Otherwise, the origin of the containing element.

The start point is offset from this origin by the value of the start coordinates (ho/vo or startho/startvo), using staff units.

Analogously, the endpoint is determined using end coordinates (endho/endvo). If endid is specified, it takes precedence over startid.

Examples of origins are:

  • staff and layer: The horizontal origin is the starting point of the measure, the vertical one is the bottom staff line;
  • note: The horizontal origin is the left end of the notehead, the vertical one is the center of the notehead;
  • clef: The horizontal origin is the left end of the clef, the vertical one the line specified by clef/line (or clef.line);
  • For elements containing text: The left end of the baseline;
  • symbolDef: As symbol definitions aren't rendered directly, their coordinate system and origin are considered virtual.

When they are referenced by symbol or altsym, the origin of the context, i.e. the referencing symbol, is used. If neither absolute nor relative coordinates are specified, determining visually suitable start and end points for line and curve attributes is left to the rendering application. A value of 0 is not always assumed for absent relative coordinates. A typical example where a rendering application may not choose the origins of absent relative start and end coordinates to be the start point as well is the line connecting two notes in the above Schumann example.

2.4.3.4Curve Shape

If neither a bezier nor bulge attribute is present, the renderer determines a suitable shape. However, if curvedir is present, the curve must respect the curvature direction specified there.

The attributes bezier and bulge define the shape of a curve in two different ways. If both are present, a rendering application may choose either one. They override curvedir.

bezier defines the inner control points of a cubic Bézier curve, i.e., a Bézier curve with two inner control points. The coordinates are given by a space separated list, first x and y offsets for the first control point, then x and y offsets for the second one. The x and y offsets are given in staff units (or inside the context of symbolDef in abstract units). The offsets for the first inner control point are relative to the start point, the ones for the second inner control point are relative to the end point.

The bulge attribute allows specification of the curve shape by a number of interpolation points. The interpolation points are given by their distance from the line connecting the start and end point. The distance values are stored as a space separated list.

The interpolation points are calculated as follows: If bulge provides n distance values, the connection line is divided into n+1 subsegments of equal length. The interpolation points are found by drawing a perpendicular line of the respective length at each subsegment joint. Positive distance values are drawn to the left of the connection line (left when traveling from start to end), negative ones to the right.

Figure 6. Rendering a bulge attribute with value \

The interpolation algorithm used by the rendering application is implementation dependent.

2.4.4Line Rendition

The form attribute of lines may take the following values:

  • dashed
  • dotted
  • solid
  • wavy

These attribute values are only qualitative. Actual dash length and dot and dash spacing are implementation dependent.

The width attribute may take the following values:

  • narrow
  • medium
  • wide

These values are also qualitative, however, they are also relative. That is, 'narrow' is the default value, 'medium' is twice as wide as 'narrow', and 'wide' is twice as wide as 'medium'.

In addition to these textual values, the width attribute may contain a numeric value and an optional unit value, "2mm" for example. If the unit value is not provided, staff interline units are presumed.

The lstartsym and lendsym attributes name the symbol that may start and/or end a line, while lstartsymsize and lendsymsize indicate the relative size of the symbol using a numeric value in the range from 1 to 9.

2.4.5Limitations

The usersymbols module does not currently support continuous composite lines or filled areas. As mentioned above, the rendition of lines is highly implementation dependent. Coordinate system transforms are restricted to scaling using scale.