Duplicate USING prefix encountered.

#2508   Compile-time warning

Duplicate USING prefix encountered.

Additional Information

The 'X' 'Y' already appears in the current list of USING prefixes.
    where X is attribute, counter, elements, referent, stream, or switch and Y is the object's name.
    or
The term 'NESTED-REFERENTS' already appears in the current list of USING prefixes.

Recovery

Compilation continues normally.

Explanation

Each object may appear at most once in any consecutive list of using prefixes.