In the first paragraph of http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#embedding-custom-non-visible-data it says that a custom data attribute is "an attribute in no namespace whose name starts with the string "data-", has at least one character after the hyphen,...". Following this, <div data-=foo> would not put anything in .dataset.
However, in the algorithm for getting the list of name-value pairs, it says to process "each content attribute on the element whose first five characters are the string "data-" and whose remaining characters (if any)...". Following this, <div data-=foo> would make .dataset[""]="foo". One of these references needs to be fixed, as webkit is implementing dataset right now. ~TJ
