background: url('foo.png')
background: url("foo/bar.jpg")

----------------------------------------------------

[
	["property-declaration", [
		["property", ["background"]],
		["punctuation", ":"],
		["url", "url('foo.png')"]
	]],
	["property-declaration", [
		["property", ["background"]],
		["punctuation", ":"],
		["url", "url(\"foo/bar.jpg\")"]
	]]
]

----------------------------------------------------

Checks for urls.