When will the Fifth Amendment privilege against self-incrimination against handwriting exemplars not be violated?

"First. The taking of the exemplars did not violate petitioner's Fifth Amendment privilege against self-incrimination. The privilege reaches only compulsion of 'an accused's communications, whatever form they might take, and the compulsion of responses which are also communications, for example, compliance with a subpoena to produce one's papers,' and not 'compulsion which makes a suspect or accused the source of "real or physical evidence" . . . .' Schmerber v. State of California, 384 U.S. 757, 763-764 (86 S.Ct. 1826, 1833, 16 L.Ed.2d 908). One's voice and handwriting are, of course, means of communication. It by no means follows, however, that every compulsion of an accused to use his voice or write compels a communication within the cover of the privilege. A mere handwriting exemplar, in contrast to the content of what is written, like the voice or body itself, is an identifying physical characteristic outside its protection. United States v. Wade, supra, 388 U.S., at 222-223 (87 S.Ct. (1926), at 1929-1930, 18 L.Ed.2d 1149). No claim is made that the content of the exemplars was testimonial or communicative matter. Cf. Boyd v. United States, 116 U.S. 616 (6 S.Ct. 524, 29 L.Ed. 746)." 388 U.S. at 266-267, 87 S.Ct. at 1953.