# Fix XLIFF file invalid from duplicate segment ids

## TL;DR

Two segments share the same id, so make every id unique. XLIFF processors key segments by id, and a duplicate makes the file invalid. Renumber or namespace the colliding ids, then validate the file before sending it anywhere.

## The error

```text
XLIFF validation error: duplicate segment id "seg-1042"
the TMS rejects the import
```

## Fix it

### Step 1: Find the duplicates

```bash
grep -o 'id="[^"]*"' file.xliff | sort | uniq -d | head -10
```

Expected: You see each duplicated id.

### Step 2: See where they collide

```bash
grep -n 'id="seg-1042"' file.xliff | head -5
```

Expected: You see the two segments sharing the id.

### Step 3: Make the ids unique

```bash
node -e "console.log('renumber the second occurrence, or prefix ids with the file or unit name they came from')"
```

Expected: Every id in the file is now unique.

### Step 4: Validate the XLIFF

```bash
xmllint --noout file.xliff && node -e "console.log('well-formed, now re-import to the TMS')"
```

Expected: xmllint passes and the TMS accepts the import.

## When to use this

- An XLIFF file is rejected for duplicate segment ids
- A merge produced colliding ids

## When NOT to use this

- The ids are unique but the file is still invalid, check the schema
- The TMS rejects for another reason, read its error

## Tool and version compatibility

- XLIFF 1.2 and 2.0, xmllint for validation
- Any TMS that validates on import

## Variant phrasings

### duplicates after merging two XLIFF files

Prefix each file's ids with a file tag before merging. Merging raw is what collides.

### duplicate unit ids rather than segment ids

Same fix at the unit level. Units need unique ids too.

## Why it happens

XLIFF uses id attributes as the primary key for segments and units. Merges, copy-paste, and generators that restart numbering all create collisions, and any validating parser rejects the file.

## Edge cases

- IDs must also be valid XML ids in some tools, avoid spaces and leading digits
- Keep a mapping of old to new ids if translations reference them
- Validate after every programmatic edit, not just at the end

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_gJvAzA38O1YrHlbS0OPOrg