XPOS is never empty — proposal

Proposal: accept the validator 0.2.8 rule (empty-string-in-xpos) as a CoNLL-U writer gate for all export targets, not only ud-next.

What exactly in mova. An unknown XPOS is written as _; an empty string is never written. This mainly concerns future languages with string XPOS (The Mova dialect: a UD metadialect, treebanks, and converters, section "Training on the metadialect"). In en, XPOS is always a PTB tag.

Why.

• the 2.19 validator will reject a file with an empty XPOS as a level 2 error;
• for 2.18 _ is also correct, so there is no loss;
• right now there is no empty XPOS anywhere: EWT, 13 other English 2.18 treebanks and corpus/mova-*-en.conllu — 0 lines (grep).

Check. This cannot be expressed in the seed rule language: it does not see raw columns. The gate is in the writer code, with a negative control: a line with an empty XPOS must produce an error.

Origin. XPOS cannot be an empty string (validator).

Mova decides.

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