Update docs and changelog.

CHANGES.md

@@ -1,6 +1,9 @@
 unreleased
 ----------
 
+- Add the `[@@@expand_inline]` transformation and support for floating attribute context
+  free transformations. (#560, @jaymody)
+
 - Export `Ast_pattern.fail`. (#563, @ceastlund)
 
 - Make `Ast_traverse.sexp_of` more concise, and add a test. (#561, @ceastlund)

doc/writing-ppxs.mld

@@ -467,6 +467,42 @@ This mechanism is implemented for derivers implemented in [ppxlib] and is conven
 
 Inline derivers will generate a [.corrected] version of the file that Dune can use to promote your file. For more information on how to use this feature to remove a dependency on [ppxlib] and a specific PPX from your project, refer to {{:https://ocaml.org/docs/metaprogramming#dropping-ppxs-dependency-with-derivinginline}this guide}.
 
+In addition to [[@@deriving_inline]], there is also [[@@@expand_inline <structure payload>]] and [[@@@expand_inline: <signature payload>]]. These can be use to inline code generated by other context free transformations (not just derivers):
+
+{@ocaml[
+  [@@@expand_inline let _ = [%add_suffix "foo"]]
+
+  let _ = "foo_suffixed"
+
+  [@@@end]
+
+  module type S = sig
+    [@@@expand_inline: type foo = [%pair_of string]]
+
+    type foo = string * string
+
+    [@@@end]
+  end
+]}
+
+In addition to [[@@deriving_inline]], there is also [[@@@expand_inline <structure payload>]] and [[@@@expand_inline: <signature payload>]]. These can be use to inline code generated by other context free transformations (not just derivers):
+
+{@ocaml[
+  [@@@expand_inline let _ = [%add_suffix "foo"]]
+
+  let _ = "foo_suffixed"
+
+  [@@@end]
+
+  module type S = sig
+    [@@@expand_inline: type foo = [%pair_of string]]
+
+    type foo = string * string
+
+    [@@@end]
+  end
+]}
+
 {1 Integration with Dune}
 
 If your PPX is written as a Dune project, you'll need to specify the [kind]