EXPath binary - subsequence()

Working though the first draft, I noticed that while |fn:subsequence()| 
and|fn:substring()| use |xs:double| for offset and length (with 
appropriate rounding),|bin:subsequence()| proposes using |xs:integer|. 
Also the former treat negative offset as working from the start, and 
'long' results are truncated to 'data end' rather than both situations 
raising errors, as proposed for |bin:subsequence()|. (I am not implying 
fractional values to pull in part octets!)

Are there any specific use cases, or other reasons, to use a different 
offset/length signature, or error regime, than is used in |fn:xxx()| ?

John
-- 
*John Lumley* MA PhD CEng FIEE
john@saxonica.com <mailto:john@saxonica.com>
on behalf of Saxonica Ltd