Chapter 14: Capability Map

Why this chapter: advanced capabilities like typed-block / @when / @for only appear in Chapter 10, with no entry point anywhere in Chapters 1–9 — readers easily conclude “SML is just what the first nine chapters show”. This chapter lays out every capability in one table: opt-in or not, five-end support, and which chapter explains it. Check here first before writing a cross-end document.

Data source: Chapter 10’s “implementation coverage table” (measured 2026-09-19) + contract mixin (2026-10-12, tasks C/D/F). The criterion is observed behavior, not source-reading; ? = not measured (does not mean absent).

Capability	Default	Rust	JS	C	C++	Lua	Chapter
Key-value / blocks / arrays / scalars	on	✅	✅	✅	✅	✅	Ch 1–2
Comments (`#` `--` `//` `/* /` `_ *_`)	on	✅	✅	✅	✅	✅	Ch 1
Bareword-as-string (`bareword-string`)	on	✅	✅	✅	✅	✅	Ch 1
`include` (single file)	on	✅	✅ ※	✅	✅	✅	Ch 4
`env` (`$env.X`)	on	✅	✅	✅	✅	✅	Ch 6
Contract (`@contract` / `@is`, single)	on	✅	✅	✅	✅	✅	Ch 5
Fragment (`@base {}` + `&base`)	on	✅ expanded	✅	⚠️ not expanded	❌	❌	Ch 3
`namespace` (`include … as ns`)	on	✅	✅	✅	✅	❌	Ch 4
`implicit-ns`	on	✅	✅	?	?	?	Ch 4
`top-level-array` (array as document root)	on	✅	❌	✅	❌	❌	Ch 10
Contract mixin (multiple contracts per block)	on※	✅	❌ `017`	❌ `017`	❌ `017`	❌ `017`	§5.4.1
`typed-block` (`Contract block { }`)	off	✅	✅	❌ silent degrade	❌	❌	§5.2.2
`@type` patterns (Loom-in-SML)	on	✅	✅	❌ explicit reject	❌ explicit reject	❌ explicit reject	§5.2.2
`multi-include` (`include "a", "b"`)	off	✅	✅	✅	✅	❌	Ch 10
`glob-include` (`include "inc/*.sml"`)	off	✅	✅	❌	?	❌	Ch 10
`regex-include` (`include "re:…"`)	off	✅	✅ (restricted subset)	?	❌	❌	Ch 10
`ext-rewrite`	off	✅	?	?	?	?	Ch 10
`@when`	off	✅	❌	❌	❌	❌	Ch 10
`@for`	off	✅	❌	❌	❌	⚠️ to re-check	Ch 10
The `@feature` gating mechanism itself	—	✅	✅	❌	❌	❌	Ch 10

※ JS resolves include from a host-supplied file map (parse(text, { files })); JS itself never touches the filesystem (designed for editor / server embedding). ※ Contract mixin needs no extra @feature (on with contract), but is currently implemented only in Rust; the other four ends explicitly report E-CONTRACT-017 (never silent).

Three quick takeaways:

Stable on all five ends (prefer for cross-end documents): key-value / blocks / arrays, comments, bareword strings, include, $env, single-contract @contract/@is, namespace.
Advanced, Rust (±JS) only: @when / @for are Rust-only; typed-block / @type / glob·regex-include are Rust + JS.
Silent or degrading — be careful across ends: C does not expand fragment; C / C++ / Lua degrade typed-block to a plain bare block; Lua’s for is pending re-check — these ends either report a code explicitly or leave a tree different from what you expect.

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