r.extendsRegistrar(...)
Overview
Section titled “Overview”r.extendsRegistrar(extensionName, def) — declares a named, globally
unique extension point that other features opt into per entity via
r.useExtension. The def can contribute onRegister, extra schema
fields (extendSchema), and entity hooks; wiring happens at registry
build time.
From packages/framework/src/engine/feature-ast/patterns.ts -> ExtendsRegistrarPattern