@altsym(optional)Provides a way of pointing to a user-defined symbol. It must contain an ID of a
                              <symbolDef> element elsewhere in the document.
                           Value conforms to  data.URI.
                            att.altsym 
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                        @copyof(optional)Points to an element of which the current element is a copy.
                           Value conforms to  data.URI.
                            att.common.anl 
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                        @corresp(optional)Used to point to other elements that correspond to this one in a generic
                              fashion.
                           One or more values from  data.URI, separated by spaces.
                            att.common.anl 
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                        @expand(optional)Indicates whether to render a repeat symbol or the source material to which it
                              refers. A value of 'true' renders the source material, while 'false' displays the
                              repeat
                              symbol.
                           Value conforms to  data.BOOLEAN.
                            att.expandable 
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                        @facs(optional)Permits the current element to reference a facsimile surface or image zone which
                              corresponds to it.
                           One or more values from  data.URI, separated by spaces.
                            att.facsimile 
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                        @fontsize(optional)Indicates the size of a font expressed in printers' points, i.e., 1/72nd of an inch,
                              relative terms, e.g., "small", "larger", etc., or percentage values relative to "normal"
                              size, e.g., "125%". 
                           Value conforms to  data.FONTSIZE.
                            att.typography 
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                        @glyphname(optional)Glyph name.
                           Value of datatype  string.
                            att.extsym 
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                        @glyphnum(optional)Numeric glyph reference in hexadecimal notation, e.g. "#xE000" or "U+E000". N.B.
                              SMuFL version 1.18 uses the range U+E000 - U+ECBF.
                           Value of datatype  
                              a string matching the following regular expression: "(#x|U\+)[A-F0-9]+"
                              .
                            att.extsym 
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                        @label(optional)Provides a name or label for an element. The value may be any string.
                           Value of datatype  string.
                            att.commonPart 
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                        @layer(optional)Identifies the layer to which a feature applies.
                           One or more values of datatype  positiveInteger, separated by spaces.
                            att.layerident 
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                        @n(optional)Provides a number-like designation for an element.
                           Value conforms to  token.
                            att.common 
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                        @next(optional)Used to point to the next event(s) in a user-defined collection.
                           One or more values from  data.URI, separated by spaces.
                            att.common.anl 
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                        @num(optional)Records a number or count accompanying a notational feature.
                           Value of datatype  positiveInteger.
                            att.numbered 
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                        @prev(optional)Points to the previous event(s) in a user-defined collection.
                           One or more values from  data.URI, separated by spaces.
                            att.common.anl 
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                        @sameas(optional)Points to an element that is the same as the current element but is not a literal
                              copy of the current element.
                           One or more values from  data.URI, separated by spaces.
                            att.common.anl 
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                        @staff(optional)Signifies the staff on which a notated event occurs or to which a control event
                              applies. Mandatory when applicable.
                           One or more values of datatype  positiveInteger, separated by spaces.
                            att.staffident 
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                        @synch(optional)Points to elements that are synchronous with the current element.
                           One or more values from  data.URI, separated by spaces.
                            att.common.anl 
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                        @tstamp(optional)Encodes the onset time in terms of musical time, i.e.,
                              beats[.fractional_beat_part].
                           Value conforms to  data.BEAT.
                            att.timestamp.musical 
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                        @tstamp.ges(optional)Captures performed onset time in several forms; that is, ppq (MIDI clicks and
                              MusicXML 'divisions'), Humdrum **recip values, beats, seconds, or mensural duration
                              values.
                           Value conforms to  data.DURATION.gestural.
                            att.timestamp.performed 
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                        @when(optional)Indicates the point of occurrence of this feature along a time line. Its value must
                              be the ID of a when element elsewhere in the document.
                           Value conforms to  data.URI.
                            att.alignment 
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                        @xml:base(optional)Provides a base URI reference with which applications can resolve relative URI
                              references into absolute URI references.
                           Value conforms to  data.URI.
                            att.commonPart 
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                        @xml:id(optional)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.
                           Value of datatype  ID.
                            att.id 
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