XO1315: `edition 2026` is the old name of `edition preview`

Before 1.0 the only edition is preview (decision 0155): nothing is frozen in the 0.x releases, and the compatibility promise of core 13 starts with the first frozen edition, which is named at 1.0. Modules written before the rename say edition 2026. That name stays an alias of preview during the 0.x releases, so they keep building, and xo check reports this note on the edition line of xo.mod. The note carries a fix that rewrites the line; xo fix (or xo check --fix) applies it.

Example

// xo.mod
module example.com/api
edition 2026

Fix

// xo.mod
module example.com/api
edition preview

Run xo explain XO1315 for this text in a terminal, or see section 10.6 of the specification.