XPOS cannot be an empty string (validator)

Gist. The validator checks something new at level 2: the XPOS column is never an empty string. An unspecified XPOS is written as _.

Level. Universal; validator (udtools 0.2.7 → 0.2.8). This change is not in changes.md: it is format, not a guideline.

Before (2.18). 2.18:tools/udtools/src/udtools/level2.py — there is no check for empty XPOS. udtools/pyproject.toml: version = "0.2.7".

Now (snapshot 24.09.2026).

• tools/udtools/src/udtools/level2.py:247–273, check_xpos_format: if cols[XPOS] == None or cols[XPOS] == '' → Error, level 2, testclass MORPHO, testid empty-string-in-xpos, «Unspecified XPOS must be encoded as an underscore ('_'), the field must not be empty.»;
• tools/udtools/src/udtools/validator.py:286 — the check is called for every token line;
• tools/udtools/pyproject.toml:7 and __init__.py: 0.2.8.

Other validator changes are only logging stubs under ###!!!, docstrings and a corrected link in a data.py message. level3.py–level6.py and validate.py did not change in substance. The tests were rewritten for the new package.

Evidence. diff -r ud-tools-v2.18/udtools tools/udtools.

What it means for English annotation. There is no empty XPOS in the EWT data, in the other 13 English 2.18 treebanks, or in corpus/mova-*-en.conllu: checked with grep, 0 lines. en writes PTB tags. The change matters for exporting mova into other languages where XPOS is a string and may be unknown: write _, not empty.

Registry. Not applicable: this is a column format. The gate must be in the CoNLL-U writer. It cannot be expressed in the seed rule language: that language does not see raw columns.

Sources. tools/udtools/src/udtools/level2.py, validator.py, pyproject.toml; 2.18:tools/udtools/….

This page in Markdown → https://md.mova.elamur.ai/free/en/docs/dialects/ud-next/seeds/xpos-not-empty/