Changelog: add #10189

readme.txt

@@ -111,6 +111,7 @@ There are opportunities for developers at all levels to contribute. [Learn more
 * Dashboard: improvements to backup interface.
 * Mobile Theme: allow one to temporary disable Jetpack's Mobile Theme for testing.
 * Mobile Theme: disable settings when feature is inactive.
+* Site Accelerator: disable a helper library by default and allow themes to enable it when required.
 * WordPress.com REST API: add flag to determine site eligibility for Full Site Editing.
 * WordPress.com synchronization: improve the reliability of the synchronization events triggered to keep your site up to date with WordPress.com.
 * WordPress.com Toolbar: update the link directing to the WordPress.com Reader.

to-test.md

@@ -4,6 +4,29 @@
 
 This release brings in significant changes to "Sync", the synchronization process that keeps your site's data up to date with WordPress.com. You'll consequently want to check that on newly connected sites as well as existing sites, data gets properly synchronized with WordPress.com. That means that features like Notifications, Publicize, Related Posts should keep working properly on your site.
 
+### Site Accelerator
+
+The devicepx library has been disabled by default, unless explicitly enabled via theme support. This library was previously used to compensate for lack of browser support. To quote Joseph Scott:
+
+```
+As a general item, I'd be happy to see devicepx go away entirely. My only concern is for places that assume it will be around and could potentially end up with unexpected results.
+
+Devicepx came about because there were not great ways for managing alternate image needs, like DPI ( retina ). Now, we have much better options that don't require JavaScript to be checking things all the time. We certainly have the browser feature support that makes it possible for devicepx to go away.
+```
+
+To test enable the Jetpack plugin. It no longer enqueues the `https://s0.wp.com/wp-content/js/devicepx-jetpack.js` script on all pages automatically.
+
+Add `add_theme_support( 'jetpack-devicepx' );` to theme's functions.php and notice that now all front-end page loads include the https://s0.wp.com/wp-content/js/devicepx-jetpack.js script. You can use the following snippet:
+
+```
+add_action( 'init', 'jetpack_declare_theme_support' );
+function jetpack_declare_theme_support() {
+	add_theme_support( 'jetpack-devicepx' );
+}
+```
+
+Load an AMP page and notice that the devicepx library is not loaded as expected.
+
 ### Others
 
 - If you have the opportunity to test in an older browser like IE11, please do so. You may catch some interesting bugs!