Added CompleteCode function.

README.md

@@ -9,7 +9,7 @@ Copyright (c) 2026 Micha Hoiting
 high-integrity identifiers. It maps a compact 32-bit integer space to a
 human-readable serial format:
 
-```
+```text
 LLL-NNN-LC
 ```
 
@@ -18,6 +18,12 @@ Where:
 - `N` = number (`100`–`999`)
 - `C` = checksum letter (`A`–`Z`)
 
+For instance 
+
+```text
+ABC-123-DT
+```
+
 ## What it provides
 
 - 4 data letters
@@ -77,6 +83,8 @@ func main() {
 	- Parses and validates `LLL-NNN-LC`, checks checksum, and returns the deterministic index.
 - `serial.Decode(idx uint32) (string, error)`
 	- Converts a valid index back to `LLL-NNN-LC`.
+- `serial.CompleteCode(codeWithoutChecksum string) (string, uint32, error)`
+	- Takes `LLL-NNN-L` and returns the completed `LLL-NNN-LC` plus index.
 - `serial.RandomCode(isInUse ...func(uint32) bool) (string, uint32, error)`
 	- Generates a random valid `LLL-NNN-LC` code and its corresponding index.
 	- If provided, the callback is used to skip indices already in use by the client.
@@ -108,6 +116,7 @@ make test
 Exported errors:
 
 - `serial.ErrInvalidFormat`
+- `serial.ErrInvalidFormatNoChecksum`
 - `serial.ErrInvalidLetters`
 - `serial.ErrForbiddenLetterTriplet`
 - `serial.ErrInvalidNumber`