Bug 2955. Workaround for lack of atomic operations in GCCE standard libraries (fall back to default use of Mutex)
<?xml version="1.0"?>
<!-- Attribute uniqueness: prefixed and unprefixed attributes with same
local name, element in same namespace as prefixed attribute -->
<foo xmlns:a="http://example.org/~wilbur">
<a:bar a:attr="1" attr="2"/>
</foo>