Clarify doc blocks.

src/Collection/CollectionInterface.php

@@ -812,13 +812,13 @@ interface CollectionInterface extends Iterator, JsonSerializable
     public function stopWhen($condition);
 
     /**
-     * Creates a new collection where the items that it will contain are the
+     * Creates a new collection where the items are the
      * concatenation of the lists of items generated by the transformer function
-     * after passing each of the items form the original collection.
+     * applied to each item in the original collection.
      *
      * The transformer function will receive the value and the key for each of the
      * items in the collection, in that order, and it must return an array or a
-     * Traversable object so that it can be concatenated to the final result.
+     * Traversable object that can be concatenated to the final result.
      *
      * If no transformer function is passed, an "identity" function will be used.
      * This is useful when each of the elements in the source collection are

src/Collection/Iterator/UnfoldIterator.php

@@ -18,8 +18,8 @@ use IteratorIterator;
 use RecursiveIterator;
 
 /**
- * An iterator that can be used to generate nested iterators out of each of
- * applying an function to each of the elements in this iterator.
+ * An iterator that can be used to generate nested iterators out of a collection
+ * of items by applying an function to each of the elements in this iterator.
  *
  * @internal
  * @see Collection::unfold()