<source>

The video, audio and picture elements can all contain source elements. Should be straight-forward, you think? This little element may have more to tell than you think. What is the history? What were the design mistakes for video that we didn't want to repeat for picture? What is the processing model for video vs. picture? Why can't you use the media attribute for video source? Why do double downloads happen? Why do people use conditional comments in their pictures? Why doesn't source with picturefill work on Android 2.3? Why is parsing the srcset attribute so complex and not just splitting on commas? Just how much can you do with this element? What are the future plans? Why are there so many questions? (Disclaimer: I might not have enough time to cover all of this!)