Serialization "ignoring or treating as empty"

In "11.3.2.4 Serialization as application/x-www-form-urlencoded":

XForms 1.1 had:

> Each element node is visited in document order, except non-relevant
elements are skipped

XForms 2.0 has:

> Each element node is visited in document order, ignoring or treating as
empty non-relevant elements

Is "ignoring" or "treating as empty" the same thing as "skipped"? I don't
know what "treating as empty" would mean. We should clarify this.

-Erik