Property anyIsValue : Boolean; (Read/Write)
This is a consequence of the mapping from CDA data types to ISO 21090. If the interval is represented as <x value="time"> then any will be populated and anyIsValue will be set to true. If, however, the interval is encoded as <x><center value="time"/></x> (which has the same meaning), then anyIsValue wil be set to true. The two forms are semantically equivalent; this attribute exists to control the xml rendition only.
Note that center in CDA is mapped to Any in ISO 21090. This is somewhat equivocal, but it appears that if matches the general intent of the somewhat odd construct of only specifying a center.