Remove an extra are.

These globally unique identifiers are called *code points* are simply numbers starting at 0.

vs.

These globally unique identifiers, called *code points*, are simply numbers starting at 0.

Author: jish

manuscript/01-The-Basics.md

@@ -6,7 +6,7 @@ ECMAScript 6 makes a large number of changes on top of ECMAScript 5. Some of the
 
 Prior to ECMAScript 6, JavaScript strings were based solely on the idea of 16-bit character encodings. All string properties and methods, such as `length` and `charAt()`, were based around the idea that every 16-bit sequence represented a single character. ECMAScript 5 allowed JavaScript engines to decide which of two encodings to use, either UCS-2 or UTF-16 (both encoding using 16-bit *code units*, making all observable operations the same). While it's true that all of the world's characters used to fit into 16 bits at one point in time, that is no longer the case.
 
-Keeping within 16 bits wasn't possible for Unicode's stated goal of providing a globally unique identifier to every character in the world. These globally unique identifiers are called *code points* are simply numbers starting at 0 (you might think of these as character codes, but there is subtle difference). A character encoding is responsible for encoding a code point into code units that are internally consistent. While UCS-2 had a one-to-one mapping of code point to code unit, UTF-16 is more variable.
+Keeping within 16 bits wasn't possible for Unicode's stated goal of providing a globally unique identifier to every character in the world. These globally unique identifiers, called *code points*, are simply numbers starting at 0 (you might think of these as character codes, but there is subtle difference). A character encoding is responsible for encoding a code point into code units that are internally consistent. While UCS-2 had a one-to-one mapping of code point to code unit, UTF-16 is more variable.
 
 The first 2^16 code points are represented as single 16-bit code units in UTF-16. This is called the *Basic Multilingual Plane* (BMP). Everything beyond that range is considered to be in a *supplementary plane*, where the code points can no longer be represented in just 16-bits. UTF-16 solves this problem by introducing *surrogate pairs* in which a single code point is represented by two 16-bit code units. That means any single character in a string can be either one code unit (for BMP, total of 16 bits) or two (for supplementary plane characters, total of 32 bits).