As a note, you don't edit privileges to view the source of an answer or question.
Simply go to the revisions of an answer/question which in this case is:
http://superuser.com/posts/211610/revisions
([SITE]/POSTS/[ID]/REVISIONS)
then click view source and it will display the actual source of the answer/question:
<kbd>shift</kbd>+<kbd>command</kbd>+<kbd>3</kbd> will work if you have escaped your VirtualBox and places the screen shot on your Mac's desktop. You could also use or <kbd>shift</kbd>+<kbd>command</kbd>+<kbd>4</kbd> which gives you a cross-hair to select the area you want to capture.