Adds a guide on bound style warning

source/deprecations/v1.x.html.md

@@ -319,6 +319,42 @@ App.instanceInitializer({
 
 Added in [PR #10256](https://github.com/emberjs/ember.js/pull/10256).
 
+#### Warning When Binding Style Attributes
+
+Content in Handlebars templates is automatically HTML-escaped to help
+developers prevent inadvertently introducing cross-site scripting (XSS)
+vulnerabilities into their applications.  If you want to display trusted
+content as HTML, you can use a `SafeString`, a special string that tells Ember
+that the content should be displayed without escaping.
+
+While this works great for HTML, there are some cases where you may bind user
+data that the browser interprets as CSS, not HTML. For example, you may bind
+the `style` attribute of an element:
+
+```handlebars
+<div style={{myStyle}}></div>
+```
+
+Handlebars only escapes HTML, not CSS, so this may introduce a potential XSS
+vulnerability into your application if a malicious user is able to provide data
+used in the `myStyle` property.
+
+Starting in Ember 1.11, you will receive a warning if you attempt to bind the
+`style` attribute of an element. Once you have verified that the content being
+displayed is trusted and properly escaped, you can disable the warning by
+making the content a `SafeString`. For example:
+
+```js
+  myStyle: function() {
+    var color = escapeCSS(this.get('color'));
+    return ("color: " + color).htmlSafe();
+  }.property('color')
+```
+
+You can learn more about `SafeString`s and writing code that prevents XSS
+attacks by reading the [Writing
+Helpers](http://emberjs.com/guides/templates/writing-helpers/) guide.
+
 ### Deprecations Added in 1.12
 
 #### Deprecate non-block-params {{each}} helper syntax