The Common category includes the following blocks: Paragraph, image, headings, list, gallery, quote, audio, cover, video. The paragraph block is the default block type. It should not have any alignment
Really cool to read through and find so much awesomeness added to WordPress 3.6 while I was gone. I should take three weeks off more often. — Andrew Nacin (@nacin)
Button blocks are not semantically buttons, but links inside a styled div. If you do not add a link, a link tag without an anchor will be used. Check to