The README says what the collector touches, and what a dyn is

README.md

@@ -10,7 +10,7 @@
 
 Flan is an experimental, ahead-of-time compiled Lisp for programs that need
 predictable memory use and a fast edit–run loop. It combines S-expressions,
-static types, explicit ownership, and a development session that can replace a
+static types, explicit allocation, and a development session that can replace a
 function in a running program without resetting its state.
 
 It is being built around games, but the interesting part is broader: a compiled
@@ -18,22 +18,28 @@ language where the running program remains available for inspection,
 experimentation, and small changes.
 
 In practical terms: you get parentheses, a debugger that would like to have a
-conversation, and no garbage collector quietly choosing the dramatic moment to
-join your frame loop.
+conversation, and a collector that only ever touches values you asked to be
+dynamic.
 
 ## What it has
 
 - Native compilation through LLVM, plus an in-progress direct x86-64 backend.
 - C-like data layout: structs, fixed arrays, pointers, slices, and explicit
-  allocation. There is no garbage collector.
-- Owned `Vec` and `Map` containers, plus checked moves and borrowing-oriented
-  slice operations.
+  allocation.
+- `Vec` and `Map` containers that take the allocator they are to use, plus
+  slices as the non-owning view of them.
 - Generics, algebraic unions, enums, macros, packages, `defer`, and a C FFI.
 - Conditions and restarts for recoverable failures and interactive debugging.
 - A raylib package and a collection of ported raylib examples.
 - Native, WASI, and web build targets. The cross targets are useful but less
   complete than the native development workflow.
 
+There is also a `dyn` type: one machine word whose contents the runtime knows
+and the type checker does not. Writing `dyn` is how a value opts in to being
+dynamic, and those values — and only those — live on a collected heap. A
+program that writes it nowhere pays nothing for it, and `--no-gc` is how to
+have that checked: it names every `dyn` in the program and refuses to build.
+
 The project is exploratory software, not a stable language release. Some
 features are deliberately refused while their semantics are still undecided;
 the compiler aims to say why rather than quietly accepting a partial version.