Document boolean attributes in JSX

docs/02.1-jsx-in-depth.md

@@ -176,6 +176,20 @@ var person = React.createElement(
 );
 ```
 
+### Boolean Attributes
+
+Omitting the value of an attribute causes JSX to treat it as `true`. To pass `false` an attribute expression must be used. This often comes up when using HTML form elements, with attributes like `disabled`, `required`, `checked` and `readOnly`.
+
+```javascript
+// These two are equivalent in JSX for disabling a button
+<input type="button" disabled />;
+<input type="button" disabled={true} />;
+
+// And these two are equivalent in JSX for not disabling a button
+<input type="button" />;
+<input type="button" disabled={false} />;
+```
+
 ### Child Expressions
 
 Likewise, JavaScript expressions may be used to express children: