Selector that filters files based on whether they are newer than a matching file in another directory tree. It can contain a mapper element, so isn't available as an ExtendSelector (since those parameters can't hold other elements).
Check to see whether any DataType we hold references to is included in the Stack (which holds all DataType instances that directly or indirectly reference this instance, including this instance itself).
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Selector that filters files based on whether they are newer than a matching file in another directory tree. It can contain a mapper element, so isn't available as an ExtendSelector (since those parameters can't hold other elements).