The sequence of
RecordReferenceand RecordSequenceobjects that exist in the sequence.
Ensure that if the first Record in the Sequence is optional, the Record has an identifier (i.e. leading data).
Examine children to work out which identifiers will trigger this particular sequence
Helper method to indicate whether the element will appear a known number of times. If the element is not required, or may appear a variable number of times, this method will return 0.