syntax_data: {"ast_node_type":"other","tokens":[{"end":84,"kind":"keyword","start":0,"text":"impl<S:"}]}
source_snippet: impl<S: Copy, X: Iterator<Item = (Byte, S)>, Y: Iterator<Item = (Byte, S)>> Iterator
context_before: // FIXME(jswrenn) we'd likely benefit from specializing try_fold here.
context_after:     for UnionIter<X, Y>