[FO31] map:entry superfluous?

Hi,
the documentation for map:entry
<https://www.w3.org/XML/Group/qtspecs/specifications/xpath-functions-31/html/#func-map-entry>
says:

Unlike the map expression (map{...}), this technique can be used to
construct a map with a variable number of entries, for example:
    map:merge(for $b in //book return map:entry($b/isbn, $b))

At least with Saxon-HE 9.7.0.8J you can achieve the same result with a
simple map constructor
    map:merge(for $b in //book return map{$b/isbn: $b})

I wonder, if this is just a "special feature" of Saxon or if there is any
other reason to keep map:entry in the proposal

salute
Th. Fischer