Address @dabrahams’s feedback

Author: natecook1000

stdlib/public/core/Arrays.swift.gyb

@@ -170,7 +170,7 @@ if True:
 """
   elif Self == 'Array':
     SelfDocComment = '''\
-/// An ordered, random-access collection of elements of a single type.
+/// An ordered, random-access collection.
 ///
 /// Arrays are one of the most commonly used data types in an app. You use
 /// arrays to organize your app's data. Specifically, you use the `Array` type

stdlib/public/core/Character.swift

@@ -21,8 +21,8 @@
 /// count the length of a string.
 ///
 ///     let greeting = "Hello! 🐥"
-///     print("Character count: \(greeting.count)")
-///     // Prints "Character count: 8"
+///     print("Length: \(greeting.count)")
+///     // Prints "Length: 8"
 ///
 /// Because each character in a string can be made up of one or more Unicode
 /// code points, the number of characters in a string may not match the length

stdlib/public/core/Collection.swift

@@ -502,27 +502,23 @@ public struct IndexingIterator<
 /// ================================
 ///
 /// You can access a slice of a collection through its ranged subscript or by
-/// calling methods like `prefix(_:)` or `suffix(from:)`. A slice of a
+/// calling methods like `prefix(while:)` or `suffix(_:)`. A slice of a
 /// collection can contain zero or more of the original collection's elements
 /// and shares the original collection's semantics.
 ///
 /// The following example creates a `firstWord` constant by using the
-/// `prefix(_:)` method to get a slice of the `text` string.
+/// `prefix(where:)` method to get a slice of the `text` string.
 ///
-///     let firstWord = text.prefix(7)
+///     let firstWord = text.prefix(while: { $0 != " " })
 ///     print(firstWord)
 ///     // Prints "Buffalo"
 ///
-/// You can retrieve the same slice using other methods, such as finding the
-/// terminating index, and the using the string's ranged subscript, or by
-/// using the `prefix(upTo:)` method, which takes an index as its parameter.
+/// You can retrieve the same slice using the string's ranged subscript, which
+/// takes a range expression.
 ///
 ///     if let firstSpace = text.index(of: " ") {
 ///         print(text[..<firstSpace]
 ///         // Prints "Buffalo"
-///
-///         print(text.prefix(upTo: firstSpace))
-///         // Prints "Buffalo"
 ///     }
 ///
 /// The retrieved slice of `text` is equivalent in each of these cases.