Registries and renderers

A rendered field passes through three registries, each owned by one layer:

Registry	Layer	Maps	Created by
Engine registry	mlform/schema, runtime	kind to a definition (schema, values, validation)	createRegistry(), createBuiltinMlRegistry() from mlform/builtins
Descriptor registry	mlform/view	kind to a presenter that returns a descriptor { component, props }	createPrimitiveDescriptorRegistry(), createBuiltinDescriptorRegistry() from mlform/view
Primitive registry	mlform/primitives	descriptor component to a custom element tag	createPrimitiveRegistry(), createBuiltinPrimitiveRegistry()

A plugin fills the first two for you. You only touch the primitive registry when a presenter names a component that MLForm does not ship, as the compass field does.

Engine registry

import { createBuiltinMlRegistry } from "mlform/builtins";
import { createRegistry, defineFieldDefinition } from "mlform/schema";

const empty = createRegistry();
const builtins = createBuiltinMlRegistry().registerField(myDefinition);

Methods: registerField, registerReport, unregisterField, unregisterReport, getField, getReport, listFields, listReports. Registering an existing kind throws RegistryError. createForm requires an engine registry; createFormView and mountForm accept one as registry and copy it, so later changes do not affect existing forms.

Descriptor registry

Presenters turn a field’s config and state into a descriptor. registerField(presenter) and registerReport(presenter) add one per kind; duplicates throw. createFormView and mountForm accept descriptorRegistry. Without it they use the built-in presenters plus those added by plugins.

Primitive registry

import { createBuiltinPrimitiveRegistry } from "mlform/primitives";

const primitiveRegistry = createBuiltinPrimitiveRegistry()
  .registerField("wind-direction-field", "wind-direction-field")
  .registerReport("risk-band", "risk-band-report");

Method	Purpose
registerField(component, tagName), registerReport(component, tagName)	Map a descriptor component to a custom element.
unregisterField(component), unregisterReport(component)	Remove a mapping.
resolveField(component), resolveReport(component)	Look up a tag.
clone()	Copy for isolated changes.

Tags must be valid custom element names (lowercase, with a hyphen). A component with no mapping renders mlf-unsupported-component, which names the missing mapping. Pass the registry to mountForm, mountPrimitiveForm, or createPrimitiveAdapter as primitiveRegistry; each copies it.

Element base classes

Class	Receives	Helpers
PrimitiveFieldElement	controller, descriptor, context (ids, label, errors, required, disabled, read-only), text	props, commitValue(), commitBlur(), getControlAttributes(), renderAssistiveText()
PrimitiveReportElement	controller, descriptor, context, text, transport, request	props
PrimitiveAsyncReportElement	as above	Calls transport.submit(request) when both are set and renders the result panel, as the built-in reports do for reportTransport.

All three are Lit elements exported from mlform/primitives. Define your element with customElements.define before the form renders.