Fix claim that U in URL stands for Universal, add erratum

Author: marijnh

12_browser.txt

@@ -109,8 +109,8 @@ the ((Internet)), and have it listen on port 80, using the
 _Hypertext Transfer Protocol_ (HTTP). This protocol allows other computers
 to request documents over the ((network)).
 
-indexsee:[Universal Resource Locator,URL]
-(((URL)))Each ((document)) on the Web is named by a _Universal Resource
+indexsee:[Uniform Resource Locator,URL]
+(((URL)))Each ((document)) on the Web is named by a _Uniform Resource
 Locator_ (URL), which looks something like this:
 
 ----

html/errata.html

@@ -63,6 +63,12 @@ <h2>Chapter 11</h2>
 its parentheses distributed incorrectly. One closing parentheses from
 the second line should be moved to the end of the last line.</p>
 
+<h2>Chapter 12</h2>
+
+<p><strong>Page 209</strong> (The Web): In the third paragraph I claim
+that the U in “URL” stands for <em>Universal</em>, whereas it actual
+stands for <em>Uniform</em>.</p>
+
 <h2>Chapter 14</h2>
 
 <p><strong>Page 242</strong> (Mouse Motion¹): The example