What is the difference between a Rule 12(b)(1) jurisdictional attack and a factual attack?

"A Rule 12(b)(1) jurisdictional attack may be facial or factual. In a facial attack, the challenger asserts that the allegations contained in a complaint are insufficient on their face to invoke federal jurisdiction. By contrast, in a factual attack, the challenger disputes the truth of the allegations that, by themselves, would otherwise invoke federal jurisdiction." Safe Air for Everyone v. Meyer, 373 F.3d 1035, 1039 (9th Cir. 2004).