Webstrates are web substrates, a practical realization of shareable dynamic media under which distributability, shareability, and malleability are fundamental software principles. Webstrates blur the distinction between application and document in a way that enables users to share, repurpose, and refit software across a variety of domains, but its reliance on a central server constrains its use; it is at odds with personal and collective control of data; and limits applications to the web. We extend the fundamental principles to include interoperability and sovereignty over data and propose MyWebstrates, an implementation of Webstrates on top of a new, lower-level substrate for synchronization built around local-first software principles. MyWebstrates registers itself in the user’s browser and function as a piece of local software that can selectively synchronise data over sync servers or peer-to-peer connections. We show how MyWebstrates extends Webstrates to enable offline collaborative use, interoperate between Webstrates on non-web technologies such as Unity, and maintain personal and collective sovereignty over data. We demonstrate how this enables new types of applications of Webstrates and discuss limitations of this approach and new challenges that it reveals.

Conflict-Free Replicated Data Types (CRDTs) support decentralized collaborative editing of shared data, enabling peer-to-peer sharing and flexible branching and merging workflows. While there is extensive work on CRDTs for plain text, much less is known about CRDTs for rich text with formatting. No algorithms have been published, and existing open-source implementations do not always preserve user intent. In this paper, we describe a model of intent preservation in rich text editing, developed through a series of concurrent editing scenarios. We then describe Peritext, a CRDT algorithm for rich text that satisfies the criteria of our model. The key idea is to store formatting spans alongside the plaintext character sequence, linked to a stable identifier for the first and last character of each span, and then to derive the final formatted text from these spans in a deterministic way that ensures concurrent operations commute. We have prototyped our algorithm in TypeScript, validated it using randomized property-based testing, and integrated it with an editor UI. We also prove that our algorithm ensures convergence, and demonstrate its causality preservation and intention preservation properties.