@on

The @on keyword tags a block element with a match trigger. It is only valid as suffix metadata inside a block element.

@on works with match selectors created by [mksel: match; value] or by the [match: value] helper.

Resolution rules

When a block is resolved with a match selector:

• all elements whose @on value equals the selector's match value form the candidate pool,
• if none match, all untagged elements become the fallback pool,
• if that pool is also empty, the block raises a runtime selector error.

If the block is weighted, the final choice is made using the weights inside the selected pool. @on expressions are evaluated once when the block is prepared, not once per iteration.

Each block element may use at most one @on and one @weight. When both are present, they can appear in either order after any optional @edit prefix.

[match: foo]{yes @on foo|no @on bar|fallback}

yes

@on outside a block element is a compile-time error.