/// Mirroring is gradual: when you mirror an outer expression like `e1
/// + e2`, the references to the inner expressions `e1` and `e2` are
/// `ExprRef<'tcx>` instances, and they may or may not be eagerly
-/// mirrored. This allows a single AST node from the compiler to
+/// mirrored. This allows a single AST node from the compiler to
/// expand into one or more Hair nodes, which lets the Hair nodes be
/// simpler.
pub trait Mirror<'tcx> {