Rune Host Implementation Guide

A Rune host is any format or runtime that embeds the Rune binding protocol. This guide covers what a host must implement, what it may extend, and how to declare Rune compliance.

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Minimum Viable Host

A host at Level 0 (intent-only) must:

1. Recognise ? as a valid prefix on element attributes
2. Parse the annotation as a string literal
3. Store it alongside the element (do not discard)
4. Never execute it at runtime

That is the complete requirement for Level 0. A YAML parser that preserves ?"..." comments as structured metadata is a valid Level 0 Rune host.

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Full Compliance Checklist

Parser

• [ ] Recognises @identifier and @identifier.field as read bindings
• [ ] Recognises ~identifier as sync bindings
• [ ] Recognises !action-name and !action-name with args as act bindings
• [ ] Recognises ?"..." and ?identifier as intent annotations
• [ ] Reports RNE-001 for unrecognised sigil characters
• [ ] Reports RNE-004 for conflicting runes on the same element (@ + ~)

State Resolution

• [ ] Maintains a named state store (mutable values)
• [ ] Maintains a named computed store (derived, read-only values)
• [ ] Resolves @identifier against computed store, then state store
• [ ] Resolves ~identifier against state store only
• [ ] Reports RNE-002 for unresolved identifiers
• [ ] Reports RNE-003 for ~ binding to a computed value

Iteration

• [ ] When @identifier references a list on a collection element, iterates the list
• [ ] Within iteration scope, resolves @item.field to current item fields
• [ ] Out-of-bounds field access returns empty string (no error)

Action Dispatch

• [ ] Maintains a named action registry
• [ ] Dispatches !action-name on primary element interaction
• [ ] Passes positional arguments to action handlers
• [ ] Reports RNE-005 for wrong argument count
• [ ] Reports RNE-002 for unregistered action names

Intent Preservation

• [ ] Stores all ? annotations in an addressable intent store
• [ ] Associates each annotation with its element identifier
• [ ] Exposes intent store to tooling (query interface)
• [ ] Never strips ? annotations during build, compilation, or minification

Error Reporting

• [ ] Reports all RNE-* error codes with line/position information
• [ ] Does not silently swallow binding errors

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Declaring Host Compliance

A Rune host declares its compliance level in its own documentation:

Rune compliance: Level 3 (full)
Rune compliance: Level 0 (intent-only)
Rune compliance: Level 1 (read bindings)

Hosts that extend Rune with additional sigils or operations must declare this explicitly and ensure extensions do not conflict with @ ~ ! ?.

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Known Hosts

Host	Format	Level	Notes
Mere	.mp.html workbooks	Level 3	Origin host — reference implementation
Recall	.rc publishing documents	Planned	Level 0 → Level 3 roadmap

To register your host, open a PR adding a row to this table.