diff --git a/crypto/doc.go b/crypto/doc.go
new file mode 100644
index 0000000..16cf476
--- /dev/null
+++ b/crypto/doc.go
@@ -0,0 +1,4 @@
+// Package crypto implements "SigningMethods" and "EncryptionMethods";
+// that is, ways to sign and encrypt JWS and JWEs, respectively, as well
+// as JWTs.
+package crypto
diff --git a/jws/doc.go b/jws/doc.go
index fa2409d..165836d 100644
--- a/jws/doc.go
+++ b/jws/doc.go
@@ -1,2 +1,2 @@
-// Package jwt implements JWSs per RFC 7515
-package jose
+// Package jws implements JWSs per RFC 7515
+package jws
diff --git a/jwt/doc.go b/jwt/doc.go
index 96483fc..6004d0f 100644
--- a/jwt/doc.go
+++ b/jwt/doc.go
@@ -1,2 +1,2 @@
 // Package jwt implements JWTs per RFC 7519
-package jose
+package jwt
diff --git a/jwt/errors.go b/jwt/errors.go
index e7ed564..9271d73 100644
--- a/jwt/errors.go
+++ b/jwt/errors.go
@@ -3,6 +3,11 @@
 import "errors"
 
 var (
-	ErrTokenIsExpired   = errors.New("token is expired")
+	// ErrTokenIsExpired is return when time.Now().Unix() is after
+	// the token's "exp" claim.
+	ErrTokenIsExpired = errors.New("token is expired")
+
+	// ErrTokenNotYetValid is return when time.Now().Unix() is before
+	// the token's "nbf" claim.
 	ErrTokenNotYetValid = errors.New("token is not yet valid")
 )