Rich Text Engine¶

Operational-transformation engine for attributed text — bold, italic, links, lists, headings, anything modeled as Quill / ProseMirror / TipTap deltas.

When to use¶

WYSIWYG editors with character-level formatting.
Quill or ProseMirror / TipTap front-ends — the engine's wire format maps 1-to-1 to delta semantics.

For plain text without attributes, use the lighter Text OT engine.

Types¶

TDoc = RichTextDocument — wraps a sequence of Insert components that together represent the current document.

TOp = RichTextOp — a delta of components:

Component	Effect
`Insert(text, attributes?)`	Insert new content, optionally formatted.
`Retain(count, attributes?)`	Skip `count` characters; if `attributes` is set, apply them to that range.
`Delete(count)`	Remove `count` characters.

TextAttributes is a dictionary string → object?. A null value means clear that attribute for the range (so {"bold": null} removes bold).

Worked example¶

// Apply bold to characters 5..10 of "Hello world"
var op = new RichTextOp(new RichTextComponent[]
{
    new Retain(5),
    new Retain(5, new TextAttributes { ["bold"] = true }),
});

var newState = engine.Apply(state, op);

Transform semantics¶

When two peers format the same range concurrently:

// Alice sets italic, Bob sets color:red on the same range.
// Both attributes survive because they don't collide on the same key.
//
// Alice sets bold=true, Bob sets bold=false on the same range.
// TransformPriority.ExistingWins → Bob's pre-existing op wins.

See TransformAttributes in the source for the exact merge matrix.

Registration¶

services.AddOpStream()
    .AddEngine<RichTextDocument, RichTextOp, RichTextEngine>("rich-text");

Mapping to Quill deltas¶

Quill's Delta shape is a direct counterpart:

Quill	OpStream
`{ insert: "hi", attributes: {bold: true} }`	`new Insert("hi", new TextAttributes { ["bold"] = true })`
`{ retain: 5, attributes: {italic: true} }`	`new Retain(5, new TextAttributes { ["italic"] = true })`
`{ retain: 5, attributes: {bold: null} }`	`new Retain(5, new TextAttributes { ["bold"] = null })`
`{ delete: 3 }`	`new Delete(3)`

A client adapter typically converts the editor's native delta into a RichTextOp JSON payload before calling SendOpAsync.

Undo / redo¶

RichTextEngine.Invert(op, preState) recovers both the deleted text and the original attributes from the pre-state, so undo restores formatting exactly. Fully compatible with UndoRedoEngine; no RestampToWin override needed.

Limitations¶

Embeds (images, mentions) are opaque blobs. Treat them as a single Insert with attributes; OT semantics still work but the engine doesn't introspect their structure.
Block-level structure isn't modeled directly. If your editor sees paragraphs / headings as distinct nodes, model the block tree with Tree CRDT and use Rich Text per leaf.