[css3-regions][cssom] NamedFlowCollection as a live collection?

Hi,

In the latest version of the CSSRegions spec (http://dev.w3.org/csswg/css3-regions/#the-namedflow-interface), the NamedFlowCollection is described to be a live collection of NamedFlow objects and it is exposed as an attribute on the Document interface. Are there any use cases that require this collection to be live rather than static? Is there a guideline/preferred way to make a collection live vs static when designing the CSSOM API?

Cheers,
Mihnea