Add a bell: a point in the text that asks the client for attention

[HarryCordewener]

MarkupText.Bell() marks a point in the text where the client is asked to get someone's attention.

var line = MarkupText.Concat(MarkupText.Plain("Someone pages you"), MarkupText.Bell());

line.Render(MarkupFormat.Ansi);    // Someone pages you + U+0007
line.Render(MarkupFormat.Pueblo);  // the same
line.Render(MarkupFormat.Mxp);     // the same
line.Render(MarkupFormat.Html);    // Someone pages you<span class="ms-bell" role="alert"></span>
line.Render(MarkupFormat.Plain);   // Someone pages you

How it is carried

A bell is an event at a position, not a property of a span, and the model has no zero-length run — Wrap returns Empty for empty text, and every operation assumes a run covers real characters. So a bell rides on the single U+0007 it marks:

• that character is a real position, so slicing, concatenation and padding carry it like any other text;
• it measures zero display cells (DisplayWidth already gives every control zero), so a column holding one is not a cell narrower than its neighbours;
• the emitter writes the character rather than letting the body through, because the Html, Pueblo and MXP encodings drop control characters from text — which is also why a bell is the only way a control character reaches rendered output.

What the HTML element means — a sound, a flash, a title change, nothing — is the page's to decide, as with the ms-cmd-link anchor.

Layout

• BellMarkup and MarkupText.Bell() are in the core package, so the type and its serialization are format-neutral; the serializer handles it beside NeutralMarkup, with no codec needed.
• The emitters are in MarkupString.Ansi, which already owns the ms-* classes and the HTML emitter for AnsiMarkup.

Tests

BellTests (6): written for every client that reads one; a control character in ordinary text still dropped; nothing left behind in Plain and BBCode; measures zero; survives Substring and Pad; round-trips through the serializer. 611/611 pass in Release.

Suggested release: 2.3.0.

🤖 Generated with Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 4d85fb4 and 96d2357.

📒 Files selected for processing (10)

• CHANGELOG.md
• MarkupString.Ansi/AnsiRegistration.cs
• MarkupString.Ansi/Emitters/BellEmitter.cs
• MarkupString.Ansi/PublicAPI.Unshipped.txt
• MarkupString.Tests/BellTests.cs
• MarkupString/BellMarkup.cs
• MarkupString/MarkupText.cs
• MarkupString/MarkupTextSerializer.cs
• MarkupString/PublicAPI.Unshipped.txt
• docs/formats.md

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