# Is `self` a SHA-1 hexdigest?
	#
	#~~~nit
	# assert "2FD4E1C67A2D28FCED849EE1BB76E7391B93EB12".is_sha1_digest
	# assert not "Not a digest".is_sha1_digest
	# assert not "2FD4E1C67A2D28FCED849EE1B76E7391B93EB12".is_sha1_digest
	# assert not "2FD4E1C67A2D28FCED849EE1UB76E7391B93EB12".is_sha1_digest
	#~~~
	fun is_sha1_digest: Bool do return length == 40 and is_hex