# Reflect.4. Preserving keyed rows — Mercury LMS

> Contract: `@fiberfx/reflect` 4.1.1; Hypergraph and Hyperscript 4.1.1.

## Contract

list({source, view, getKey?, mapItem?, bind?, mapProps?, hooks?}) returns a component. Source holds a readonly-compatible array. Stable keys preserve row DOM/local state; index is positional identity when getKey is absent.

mapItem replaces item props. Functions it returns are scope-bound; raw function-valued direct item props are also wrapped. Required row props must be covered. mapItem/mapProps overlap refuses. Union views require complete items or one correlated item prop.

## Keys and refusals

String normalization makes 1 and "1" duplicates, but leaves "01" distinct. Reject invalid keys, non-array state, primitive items without mapping. Verify package failures in a test. The [lab](/examples/reflect-lab/index.html?part=lists&lang=en) refuses duplicates in an application preflight, not by catching list's renderer exception.

## Observation

Check Alpha, reverse, remove Beta: Alpha stays checked and changes position. Assert DOM identity separately. Removing and restoring a row starts fresh local state. Whole-exercise restart clears local state; merely resetting model data need not.

## Navigation

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