Return one of the prefixes mapped to a Namespace URI.

If more than one prefix is currently mapped to the same URI, this method will make an arbitrary selection; if you want all of the prefixes, use the getPrefixes method instead.

Note: this will never return the empty (default) prefix; to check for a default prefix, use the getURI method with an argument of "".

Parameters:

uri the namespace URI

Returns: one of the prefixes currently mapped to the URI supplied, or null if none is mapped or if the URI is assigned to the default namespace