Several important vendor prefixes are missing
In some cases, such as the CSS flexbox's "order" attribute, WE2015 knows there are vendor prefixes needed (see https://s24.postimg.org/po0dgiodh/vendor_prefixes.jpg for example). However, it doesn't actually let you *insert* those prefixes. I now either have to just know those prefixes or go look them up.
In an other case, "display: flex;", WE2015 doesn't even recognize the need for vendor prefixes, even though it will break in as recent a browser as IE 10.
These missing prefixes leave several "blind spots" that I don't see until I conduct cloud testing.