<when>

<when> indicates a point in time either relative to other elements in the same timeline tag, or absolutely. [16.4.2 Placing Synchronous Events in Time]
Module linking — Linking, Segmentation, and Alignment
Attributes att.global (@xml:id, @n, @xml:lang, @xml:base, @xml:space) (att.global.rendition (@rend, @style, @rendition)) (att.global.linking (@corresp, @synch, @sameAs, @copyOf, @next, @prev, @exclude, @select)) (att.global.analytic (@ana)) (att.global.facs (@facs)) (att.global.change (@change)) (att.global.responsibility (@cert, @resp)) (att.global.source (@source))
absolute⚓︎ supplies an absolute value for the time.
Status Optional
Datatype teidata.temporal.w3c
Note

This attribute should always be specified on a when element which serves as the target for the origin attribute of a timeline.
unit⚓︎ specifies the unit of time in which the interval value is expressed, if this is not inherited from the parent timeline.
Status Optional
Datatype teidata.enumerated
Suggested values include:
d
(days)
h
(hours)
min
(minutes)
s
(seconds)
ms
(milliseconds)
interval⚓︎ specifies a time interval either as a number or as one of the keywords defined by the datatype teidata.interval
Status Optional
Datatype teidata.interval
since⚓︎ identifies the reference point for determining the time of the current when element, which is obtained by adding the interval to the time of the reference point.
Status Optional
Datatype teidata.pointer
Note

This attribute should point to another when element in the same timeline. If no value is supplied, and the absolute attribute is also unspecified, then the reference point is understood to be the origin of the enclosing timeline tag.
Contained by
linking: timeline
May contain Empty element
Note

On this element, the global xml:id attribute must be supplied to specify an identifier for this point in time. The value used may be chosen freely provided that it is unique within the document and is a syntactically valid name. There is no requirement for values containing numbers to be in sequence.
Example
<when xml:id="TW3" interval="20" since="#w2"/>
Content model 
<content>
 <empty/>
</content>
Schema Declaration 
<rng:element name="when">
 <rng:ref name="att.global.attributes"/>
 <rng:ref name="att.global.rendition.attributes"/>
 <rng:ref name="att.global.linking.attributes"/>
 <rng:ref name="att.global.analytic.attributes"/>
 <rng:ref name="att.global.facs.attributes"/>
 <rng:ref name="att.global.change.attributes"/>
 <rng:ref name="att.global.responsibility.attributes"/>
 <rng:ref name="att.global.source.attributes"/>
 <rng:optional>
  <rng:attribute name="absolute">
   <rng:ref name="teidata.temporal.w3c"/>
  </rng:attribute>
 </rng:optional>
 <rng:optional>
  <rng:attribute name="unit">
   <rng:choice>
    <rng:value>d</rng:value>
    <rng:value>h</rng:value>
    <rng:value>min</rng:value>
    <rng:value>s</rng:value>
    <rng:value>ms</rng:value>
    <rng:ref name="teidata.enumerated"/>
   </rng:choice>
  </rng:attribute>
 </rng:optional>
 <rng:optional>
  <rng:attribute name="interval">
   <rng:ref name="teidata.interval"/>
  </rng:attribute>
 </rng:optional>
 <rng:optional>
  <rng:attribute name="since">
   <rng:ref name="teidata.pointer"/>
  </rng:attribute>
 </rng:optional>
 <rng:empty/>
</rng:element>
element when
{
   att.global.attributes,
   att.global.rendition.attributes,
   att.global.linking.attributes,
   att.global.analytic.attributes,
   att.global.facs.attributes,
   att.global.change.attributes,
   att.global.responsibility.attributes,
   att.global.source.attributes,
   attribute absolute { teidata.temporal.w3c }?,
   attribute unit { "d" | "h" | "min" | "s" | "ms" | teidata.enumerated }?,
   attribute interval { teidata.interval }?,
   attribute since { teidata.pointer }?,
   empty
}