All or nothing. For example, if you wanted to buy 25,000 shares at .02, there would have to be at least that amount available for that price. If there was less, your order wouldn't be filled until there was 25,000 shares offered for sale at .02. Also, you would have to be the first in line to get the stock at .02.
I don't use AON because I will accept a partial fill at the price I set. The downside is that MMs can piecemeal your order.