REFERENCE.md owns capitalization, controls, messages, links, placeholders, inclusion.

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Sentence case; front-load object/result.
Labels, helpers, placeholders, tooltips, errors each have one job.
Buttons name action+object, not Yes/No/Submit/OK/Done.
Errors give cause, constraint, recovery; empty states give reason and one next step.
Labels persist; placeholders are examples only.
Completion toasts use subject + past-tense verb.
Use please/sorry/thanks only for real inconvenience.
Name permanent destructive loss directly.
Keep regex and validation messages adjacent.
Stress localization length, numbers, offline/error, truncation, recovery.

Use project glossary and canonical product names. Code escape: // allow: ux-copy [reason].