Chapter 2. Writing a Module, Page 20

Location on the page: 
Second line
Chapter: 
2. Writing a Module
Error: 

if (!in_array($node->type, $types_to_annotate)) {

Correction: 

if (!in_array($node->type, $types_to_annotate, TRUE)) {

Description of the Error: 

Also on page 26, middle of page.

Strict mode for in_array() must be used or the if will fail and thus the annotation form would be displayed on nodes of all types, not just the types selected in Home / Administer / Node annotation. [Fixed in downloadable code.]