HTML5 has a new global attribute, hidden, which can be used to hide content.

CSS has the display:none rule, which can also be used to hide content.

article { display:none; }

Visually, they are identical. What is the difference semantically? Computationally?

What guidelines should I consider on when to use one or the other?

TIA.

EDIT: Based on @newtron's responses (below), I did more searching. The hidden attribute was hotly contested last year and (apparently) barely made it into the HTML5 spec. Some argued it was redundant and had no purpose. From what I can tell, the final evaluation is this: If I'm targeting only web browsers, there is no difference. (One page even asserted that web browsers used display:none to implement the hidden attribute.) But if I'm considering accessibility (e.g., perhaps I expect my content to be read by screen-readers), then there is a difference. The CSS rule display:none might hide my content from web browsers, but a corresponding aria rule (e.g., aria-hidden="false") might try to read it. Thus, I now agree that @newtron's answer is correct, though perhaps (arguably) not as clear as I might like. Thanks @newtron for your help.