[css3 images] ambiguous form of radial gradient

The radial gradient syntax at <http://dev.w3.org/csswg/css3-images/#radial-gradients> is:

<radial-gradient>
= radial-gradient(
	[<bg-position>,]? 
	[
		[<shape> || <size>]
		|
		[<length> | <percentage>]{2}
	,]? 
	<color-stop>[, <color-stop>]+
)

This allows for some ambiguity with a gradient like:

 background-image: radial-gradient(10% 10%, blue, green);

since it's unclear if the first two <length> values refer to
the <bg-position>, or to the [<length> | <percentage>]{2}.

Simon