Corrected minimum stated width in comment for largest picture
…and generated the child img element if it's not already present. With this tweak in place, the picture markup pattern supports non-js fallbacks, avoids prefetch, and enjoys all benefits of the proposed picture element functionality. Production ready, perhaps.
Exit early if picture is natively supported.
…this point). If Modernizr is available, add a test for picture to it (adds handy picture/no-picture classes to HTML element). Also uses Modernizr's mq shim if available. Both these enhancements do NOT REQUIRE Modernizr and take just a few lines to implement.