+
+ # 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