The dis and dis.place attributes record the amount and direction of displacement, respectively. The lform and lwidth attributes capture the appearance of the continuation line associated with the octave displacement. The starting point of the octave displacement may be indicated by either a startid, tstamp, tstamp.ges, or tstamp.real attribute, while the ending point may be recorded by either a dur, dur.ges, endid, or tstamp2 attribute. It is a semantic error not to specify one starting and one ending type of attribute. Also, note that the dur attribute is not required because the octave displacement can be visually instantaneous.
                                 <elementSpec ident="octave" module="MEI.cmn">
                                    
                                    <desc xml:lang="en">An indication that a passage should be performed one or more octaves above or below
                                       its
                                       written pitch.</desc>
                                    
                                    <classes>
                                       
                                       <memberOf key="att.common"/>
                                       
                                       <memberOf key="att.facsimile"/>
                                       
                                       <memberOf key="att.octave.log"/>
                                       
                                       <memberOf key="att.octave.vis"/>
                                       
                                       <memberOf key="att.octave.ges"/>
                                       
                                       <memberOf key="att.octave.anl"/>
                                       
                                       <memberOf key="model.controlEventLike.cmn"/>
                                       </classes>
                                    
                                    <content>
                                       
                                       <rng:zeroOrMore>
                                          
                                          
                                          </rng:zeroOrMore>
                                       </content>
                                    
                                    <constraintSpec ident="octave_start-_and_end-type_attributes_required" scheme="schematron">
                                       
                                       <constraint>
                                          
                                          <sch:rule context="mei:octave">
                                             
                                             <sch:assert test="@startid or @tstamp or @tstamp.ges or @tstamp.real">Must have one of the
                                                attributes: startid, tstamp, tstamp.ges or tstamp.real.</sch:assert>
                                             
                                             <sch:assert test="@dur or @dur.ges or @endid or @tstamp2">Must have one of the attributes:
                                                dur, dur.ges, endid, or tstamp2.</sch:assert>
                                             </sch:rule>
                                          </constraint>
                                       </constraintSpec>
                                    
                                    <remarks xml:lang="en">
                                       
                                       <p>The <att>dis</att> and <att>dis.place</att> attributes record the amount and direction of
                                          displacement, respectively. The <att>lform</att> and <att>lwidth</att> attributes capture
                                          the appearance of the continuation line associated with the octave displacement. The
                                          starting point of the octave displacement may be indicated by either a <att>startid</att>,
                                          <att>tstamp</att>, <att>tstamp.ges</att>, or <att>tstamp.real</att> attribute, while the
                                          ending point may be recorded by either a <att>dur</att>, <att>dur.ges</att>,
                                          <att>endid</att>, or <att>tstamp2</att> attribute. It is a semantic error not to specify one
                                          starting and one ending type of attribute. Also, note that the <att>dur</att> attribute is
                                          not required because the octave displacement can be visually instantaneous.</p>
                                       </remarks>
                                    </elementSpec>