Added missing documentation

error.go

@@ -1,21 +1,45 @@
 package uuid
 
+// Error is a custom error type for UUID-related errors
 type Error string
 
+// The strings defined in the errors is matching the previous behavior before
+// the custom error type was implemented. The reason is that some people might
+// be relying on the exact string representation to handle errors in their code.
 const (
-	ErrInvalidFormat           = Error("uuid: invalid UUID format")
+	// ErrInvalidFormat is returned when the UUID string representation does not
+	// match the expected format. See also ErrIncorrectFormatInString.
+	ErrInvalidFormat = Error("uuid: invalid UUID format")
+
+	// ErrIncorrectFormatInString can be returned instead of ErrInvalidFormat.
+	// A separate error type is used because of how errors used to be formatted
+	// before custom error types were introduced.
 	ErrIncorrectFormatInString = Error("uuid: incorrect UUID format in string")
-	ErrIncorrectLength         = Error("uuid: incorrect UUID length")
-	ErrIncorrectByteLength     = Error("uuid: UUID must be exactly 16 bytes long")
-	ErrNoHwAddressFound        = Error("uuid: no HW address found")
-	ErrTypeConvertError        = Error("uuid: cannot convert")
-	ErrInvalidVersion          = Error("uuid:")
+
+	// ErrIncorrectLength is returned when the UUID does not have the
+	// appropriate string length for parsing the UUID.
+	ErrIncorrectLength = Error("uuid: incorrect UUID length")
+
+	// ErrIncorrectByteLength indicates the UUID byte slice length is invalid.
+	ErrIncorrectByteLength = Error("uuid: UUID must be exactly 16 bytes long")
+
+	// ErrNoHwAddressFound is returned when a hardware (MAC) address cannot be
+	// found for UUID generation.
+	ErrNoHwAddressFound = Error("uuid: no HW address found")
+
+	// ErrTypeConvertError is returned for type conversion operation fails.
+	ErrTypeConvertError = Error("uuid: cannot convert")
+
+	// ErrInvalidVersion indicates an unsupported or invalid UUID version.
+	ErrInvalidVersion = Error("uuid:")
 )
 
+// Error returns the string representation of the UUID error.
 func (e Error) Error() string {
 	return string(e)
 }
 
+// Is checks if the target error is a UUID Error
 func (e Error) Is(target error) bool {
 	_, ok := target.(*Error)
 	return ok