FALSE negative: www.google.de

[ffischer1984]

IMHO it should be an url ;)

[davisjam]

www.google.com is also not a URL.

From the source:

/**
 * RegExps.
 * A URL must match #1 and then at least one of #2/#3.
 * Use two levels of REs to avoid REDOS.
 */

var protocolAndDomainRE = /^(?:\w+:)?\/\/(\S+)$/;

I believe this project follows the definition of URL given in RFC 1738 (relevant bit).