XSLT3.0: Predictable recovery of errors when rollback

In section 8.3 "Recovery of Result Trees"  of the 2nd Last Call of the
W3C XSLT 3.0 specification
(http://www.w3.org/TR/2014/WD-xslt-30-20141002/#recovery), we read:

"When rollback-output="no" is specified, it is still possible to
ensure recovery of errors happens predictably by evaluating the
potentially-failing code in temporary output state: typically, within
an xsl:variable. In effect the variable acts as an explicit buffer for
temporary results, which is only copied to the final output if
evaluation succeeds."

I feel rather confused by this statement. There is no example, backing
it, provided and my attempts to construct such an example were not
successful. I am beginning to think that the quoted statement above
may not be true.

In particular, how would one verify whether or not an error occurred
(and was caught) when producing the result tree contained in a
particular variable? Knowing this is needed in order to decide whether
to output this variable to the final output or not.

My question/request is for anyone to provide such an example.

And the document will gain a lot by including such example in it.

-- 
Cheers,
Dimitre Novatchev
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