Insert and safely resolve variables in Lexxy rich text. The gem gives you an editor button (and a `{{` prompt) for inserting variables, each stored as an Action Text attachment chip rather than literal markup. `with_variables` resolves the chips and returns plain Action Text content. Register new chip types with `register_attachment`. A :text chip resolves to an escaped string, an :html chip splices rich content in before sanitization. Liquid is optional. The default renderer is plain, injection-safe string substitution and pulls in no template engine.