[foo]: http://prismjs.com
[foo]: http://prismjs.com "foo\"bar"
[foo]: http://prismjs.com 'foo\'bar'
![foo]: http://prismjs.com (foo (bar\) baz)
[foo]: <http://prismjs.com> "Prism"

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

[
	["url-reference", [
		["punctuation", "["],
		["variable", "foo"],
		["punctuation", "]"],
		["punctuation", ":"],
		" http://prismjs.com"
	]],
	["url-reference", [
		["punctuation", "["],
		["variable", "foo"],
		["punctuation", "]"],
		["punctuation", ":"],
		" http://prismjs.com ",
		["string", "\"foo\\\"bar\""]
	]],
	["url-reference", [
		["punctuation", "["],
		["variable", "foo"],
		["punctuation", "]"],
		["punctuation", ":"],
		" http://prismjs.com ",
		["string", "'foo\\'bar'"]
	]],
	["url-reference", [
		["punctuation", "!"],
		["punctuation", "["],
		["variable", "foo"],
		["punctuation", "]"],
		["punctuation", ":"],
		" http://prismjs.com ",
		["string", "(foo (bar\\) baz)"]
	]],
	["url-reference", [
		["punctuation", "["],
		["variable", "foo"],
		["punctuation", "]"],
		["punctuation", ":"],
		["punctuation", "<"],
		"http://prismjs.com",
		["punctuation", ">"],
		["string", "\"Prism\""]
	]]
]

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

Checks for URL references.