🖋️ NABU — Next-Generation Block Engine

Nabu is a modular, local-first block editor engine built on a Single ContentEditable architecture. It bridges the gap between the intuitive selection of document-based editors (Google Docs, ProseMirror) and the structural flexibility of block-based editors (Notion).

🏗️ Core Architecture

Single ContentEditable Root

Unlike traditional block editors that use isolated editable zones, Nabu manages a single native selection at the root. This guarantees seamless cross-block selection, native copy-paste, and superior browser performance.

Reactive CRDT Core (Loro-CRDT)

Nabu treats the UI as a pure reflection of a distributed state. Built on Loro-CRDT (WASM), it provides out-of-the-box support for:

• Local-First: High-performance local state with offline-first capabilities.
• Collaboration: Conflict-free merging of concurrent edits.
• Rich Text: Native support for spans and marks via Loro Deltas.

Svelte 5 Integration

Leveraging Svelte 5's Runes ($state, $derived), Nabu achieves fine-grained reactivity. Only modified blocks or selection states trigger re-renders, ensuring a fluid 60fps experience even in massive documents.

🛠️ Key Technical Features

• Selection Bridge: A high-precision mapping engine between DOM Nodes/Offsets and Model IDs/Indexes, enabling stable cursor restoration and robust cross-block ranges.
• Event Ascension: A modular "Chain of Responsibility" pattern. Blocks handle local interactions while structural changes (split, merge) are escalated to parents or engine-level hooks.
• Delta-Based Mutations: All structural operations (splitting, merging) utilize Loro Deltas to preserve formatting and metadata integrity during transformation.
• Block Registry: A highly decoupled extension system allowing developers to define custom logic and UI for any block type.

🚀 Tech Stack

• UI Framework: Svelte 5
• State/CRDT: Loro-CRDT (WASM)
• Typing: Strict JSDoc
• Architecture: OOP-based Block Registry & Extensions

Architected for performance, built for the future of collaborative writing.