# `lr-mutation-observer` - **Import** `import '@aceshooting/lyra-ui/components/lr-mutation-observer.js';` (stable tag alias; registers the tag) - **Class** `LyraMutationObserver`, also available unregistered from `@aceshooting/lyra-ui/components/utility/mutation-observer/mutation-observer.class.js` - **Family** `components/utility/` — see `llms/index.md` for its siblings - **Status** `stable` since `4.0.0` — see the maturity and deprecation policy in `llms/shared.md` - **Release history** [CHANGELOG.md](../../CHANGELOG.md); family-wide breaking-change summaries: [llms-full.txt](../../llms-full.txt) - **Deprecations** none - **Optional peers** none - **Themeable via** 1 part, 0 custom properties — see this component's own `@csspart`/`@cssprop` list below - **Library-wide behavior** (events, form association, `locale`/`strings`, tokens, TS types): `llms/shared.md` --- ## `lr-mutation-observer` Lifecycle-managed wrapper around the native `MutationObserver`. All element children in the default slot are observed and their mutation records are emitted as a composed event; the wrapper itself adds no layout. **Properties:** `disabled: boolean = false` (reflected), `childList: boolean = false` (attribute `child-list`; **changed in 8.0.0** from Lyra's former `true` default, so opt in explicitly when needed; reflected), `attr: string | null = null` (reflected; `*` observes every attribute; otherwise a space-separated filter), `attrOldValue: boolean = false` (`attr-old-value`), `charData: boolean = false` (`char-data`), and `charDataOldValue: boolean = false` (`char-data-old-value`); all four mapped attributes reflect. Lyra's existing aliases remain and also reflect: `observeAttributes` (`attributes`; unfiltered boolean form of `attr`, equivalent to `attr: '*'`) and `characterData` (`character-data`, equivalent to `charData`). Plus `subtree: boolean = true`, and programmatic `attributeFilter: string[] = []` (neither reflects). The browser capability is optional. A missing or throwing owner-window lookup, or an unavailable or throwing constructor, leaves that rebuild inert rather than leaking an exception. Individual `observe` and `disconnect` failures are contained, so later valid targets and later rebuilds can still observe. Callbacks from a retired document are ignored after disconnect or adoption. `attributeFilter` is likewise a bounded own-data snapshot (examining at most its first 10,000 direct data entries); malformed or accessor-backed entries are skipped, a valid prefix remains active, and an entirely unusable value falls back to an empty filter. **Events:** `lr-mutation`; its detail and bounded readonly record sequence are frozen. `detail.records` and mapped `detail.mutationList` reference the same sequence, while each native `MutationRecord` retains identity. **Slots:** default observed elements. **CSS parts:** `base`. ---