Best Practices

Robust XTend applications come from clear ownership, small public contracts, and observable failure behavior. The following rules apply to XTend Classic hosts and Maraca/RMT app shells alike.

Start with public contracts

Integrate components through tags registered in components/manifest.json and their .d.ts declarations. Use attributes, properties, events, slots, CSS parts, and tokens; do not reach into private shadow DOM or internal state objects. A wrapper may translate a contract, but should not extend it silently.

Keep IDs, state keys, and event names stable. A change to a schema such as xtend.rmt.component-contract.v1 needs a migration or a new version, not merely an updated example.

Give work to the right owner

Canonical state belongs to the application or its responsible controller. Fabric lanes schedule work but do not own business state. A worker may normalize snapshots or prepare data, but must not take ownership of DOM or host services. For XTensions, runtime, container, and CSS remain host-owned.

Load locally and explicitly

Use XTend Classic with xtend-loader.js and a local manifest for directly authored HTML and JavaScript. Remote surfaces require an origin allowlist, integrity, capability policy, and a local fallback. Dynamic imports may resolve known modules only; a URL supplied by a user is not a module reference.

Measure rather than guess

Set budgets for mount, hydration, and interaction, then run the corresponding gates. The XTend Dev Surface makes performance, kernel, and Fabric state visible, but it does not replace a reproducible CI report. Diagnostic snapshots should identify their time base, schema, and status explicitly.

Degrade visibly

An optional adapter may fail without taking down its host. Its fallback must name the missing capability. Security, integrity, and kernel failures remain blocking; they must not be relabeled as a generic warning.

Start a new integration with the Quick Start. Before publishing, inspect the commands and reports in Release Verification.