fix

index.bs

@@ -6232,8 +6232,8 @@ There is no way to represent an async iterable value in IDL.
 <h5 id="idl-async-iterator-object" lt="async-iterator" dfn export>Async iterator objects</h5>
 
 An <dfn lt="async iterator" export>async iterator&lt;|T|&gt;</dfn> value is a reference to an object
-that can produce a sequence of values asynchronously. The async iterator value is is a parameterized
-by a type |T|, which defines the types of values produced by this async iterator.
+that can produce a sequence of values asynchronously. The async iterator value is parameterized by a
+type |T|, which defines the types of values produced by this async iterator.
 
 Async iterators, unlike sequences, do not have a fixed length and can be infinite. Values are
 asynchronously produced as the async iterator is iterated over.