Github Expanding Diffs - Great new feature

Github has added a great feature (which Bitbucket already had but I'm excited about anyway).  When you are looking at a commit/pull request or diff it only shows the code immediately around the changes but now you can tap the icon in the gutter to see more code which can be really useful to help understand the commit.

See these screenshots of an example commit to SVGtoIcons. See previous posts for information about that project.