comark/charts/duplicate-column · Give each column of a chart's table its own header

x, y, and annotations find columns by their header, so two columns with the same header can't be told apart. The block shows the table alone. This is usually a copied header that wasn't changed.

Incorrect

::chart{title="Ducks per pond"}
| pond | 2025 | 2025 |
| --- | --: | --: |
| north | 12 | 15 |
| south | 7 | 6 |
| east | 9 | 11 |
::

lint-comark example.mdexample.md:1:1 comark/charts/duplicate-column::chart 1: its table has two columns named 2025.Give each column its own name.✖ 1 problem

Correct

::chart{title="Ducks per pond"}
| pond | 2025 | 2026 |
| --- | --: | --: |
| north | 12 | 15 |
| south | 7 | 6 |
| east | 9 | 11 |
::

lint-comark example.md✔ No problems