diff --git a/Cargo.lock b/Cargo.lock
index f090e1f..b005172 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1383,7 +1383,9 @@ name = "synthizer_macros_internal"
 version = "0.1.0"
 dependencies = [
  "darling",
+ "ident_case",
  "proc-macro-error",
+ "proc-macro2",
  "quote",
  "syn 2.0.38",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 74260cb..154e7ca 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,6 +16,7 @@ derive_more = "0.99.17"
 enum_dispatch = "0.3.12"
 env_logger = "0.10.0"
 eye_dropper = { path = "crates/eye_dropper" }
+ident_case = "1.0.1"
 im = "15.1.0"
 itertools = "0.10.5"
 lazy_static = "1.4.0"
diff --git a/crates/synthizer_macros_internal/Cargo.toml b/crates/synthizer_macros_internal/Cargo.toml
index f5cae64..4175954 100644
--- a/crates/synthizer_macros_internal/Cargo.toml
+++ b/crates/synthizer_macros_internal/Cargo.toml
@@ -10,6 +10,8 @@ proc-macro = true
 
 [dependencies]
 darling.workspace = true
+ident_case.workspace = true
+proc-macro2.workspace = true
 proc-macro-error.workspace = true
 quote.workspace = true
 syn.workspace = true
diff --git a/crates/synthizer_macros_internal/src/lib.rs b/crates/synthizer_macros_internal/src/lib.rs
index 40ae8be..0d5332e 100644
--- a/crates/synthizer_macros_internal/src/lib.rs
+++ b/crates/synthizer_macros_internal/src/lib.rs
@@ -5,3 +5,17 @@
 //! lot of boilerplate abstraction, for example understanding the concept of a property and building node descriptors.
 //! Rather than type this tens of times and refactor them all tens of times per change, we have this crate to help us
 //! out.
+//!
+//! This crate contains dummy forwarders at the root to let us split it into files. See the individual modules for docs
+//! on the macro. Procmacro limitations currently require that they be at the root.
+mod property_slots_impl;
+mod utils;
+
+#[proc_macro_attribute]
+#[proc_macro_error::proc_macro_error]
+pub fn property_slots(
+    attrs: proc_macro::TokenStream,
+    body: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    property_slots_impl::property_slots_impl(attrs.into(), body.into()).into()
+}
diff --git a/crates/synthizer_macros_internal/src/property_slots_impl.rs b/crates/synthizer_macros_internal/src/property_slots_impl.rs
new file mode 100644
index 0000000..b562296
--- /dev/null
+++ b/crates/synthizer_macros_internal/src/property_slots_impl.rs
@@ -0,0 +1,138 @@
+//! A macro to handle PropertyCommandReceiver, which we apply to XXXSlots structs. This does two things:
+//!
+//! - Implements PropertyCommandReceiver.
+//! - Creates a XXXProperties struct which is for the public API of a node.
+//!
+//! Input structs *must* be named with the Slots suffix, and will be sealed magically with this macro.  See the structs
+//! in this file for input options.
+//!
+//! This is an attribute macro and not a derive because it must seal the struct, and so must have the ability to move
+//! the original definition.  All struct-level options will go in the `property_slots` attribute (also the macro
+//! invocation) and (later, when we implement options for such), field options will be `slot`.
+//!
+//! To document properties, document them on the input struct.  The docs are then copied over to the output and (in
+//! future) augmented with additional metadata such as ranges.
+//!
+//! It is strictly assumed that all fields of a slots struct are `PropertySlot<Marker>`.
+use darling::{FromDeriveInput, FromField};
+use syn::parse::Parse;
+use syn::spanned::Spanned;
+
+// Note that we can get a DeriveInput from an attribute macro simply by ignoring the attribute token stream.
+
+#[derive(Debug, FromDeriveInput)]
+#[darling(supports(struct_named))]
+struct PropSlotsInput {
+    ident: syn::Ident,
+    data: darling::ast::Data<(), syn::Field>,
+}
+
+pub(crate) fn property_slots_impl(
+    _attrs: proc_macro2::TokenStream,
+    body: proc_macro2::TokenStream,
+) -> proc_macro2::TokenStream {
+    let syn_input: syn::DeriveInput = match syn::parse2(body.clone()) {
+        Ok(x) => x,
+        Err(e) => proc_macro_error::abort_call_site!(e),
+    };
+
+    let input = match PropSlotsInput::from_derive_input(&syn_input) {
+        Ok(x) => x,
+        Err(e) => {
+            return e.write_errors().into();
+        }
+    };
+
+    if !input.ident.to_string().ends_with("Slots") {
+        proc_macro_error::abort!(input.ident, "Slot struct names must end with 'Slots'");
+    }
+
+    // The input to this macro is already a complete slots struct; sep 1 is to seal it.
+    let sealed_slots = crate::utils::seal(&input.ident, &body);
+
+    // Step 2 is to generate a struct for the public API, of the form XxxProperties.  We do this in three steps:
+    //
+    // 1. Figure out the identifier;
+    // 2. Figure out the declaration;
+    // 3. Figure out the PropertyCommandReceiver implementation.
+
+    let mut public_name = input
+        .ident
+        .to_string()
+        .strip_suffix("Slots")
+        .expect("We validated that it ends with slots earlier")
+        .to_string();
+    public_name.push_str("Props");
+
+    struct PropDef {
+        name: syn::Ident,
+        marker: syn::Type,
+    }
+
+    let mut fields: Vec<PropDef> = vec![];
+
+    for f in input
+        .data
+        .clone()
+        .take_struct()
+        .expect("Darling should validate this is a struct")
+        .into_iter()
+    {
+        let name = f.ident.unwrap();
+        let ty_path = match f.ty {
+            syn::Type::Path(ref p) => p.clone(),
+            _ => proc_macro_error::abort_call_site!(
+                "Found a non-struct field in this struct. Fields should always be 'Slot<Marker>'"
+            ),
+        };
+
+        let last_seg = match ty_path.path.segments.last() {
+            Some(x) => x,
+            None => {
+                proc_macro_error::abort!(
+                    f.ty.span(),
+                    "This path has no segments; it should be of the form 'Slot<MarkerHere>'"
+                );
+            }
+        };
+
+        // That last segment should have exactly one generic; that generic should be the path to a concrete marker type.
+        let args = match last_seg.arguments {
+            syn::PathArguments::AngleBracketed(ref a) => a.clone(),
+            _ => proc_macro_error::abort!(
+                last_seg.span(),
+                "This should have some generics on it, but does not"
+            ),
+        };
+
+        let args = args.args;
+
+        if args.len() != 1 {
+            proc_macro_error::abort!(args.span(), "This should have exactly one generic argument");
+        }
+
+        let marker = match args[0] {
+            syn::GenericArgument::Type(ref t) => t.clone(),
+            _ => proc_macro_error::abort!(args[0].span(), "Thios should be a type"),
+        };
+
+        fields.push(PropDef { name, marker });
+    }
+
+    // Our generic lifetime is `'a`.
+    let public_field_decls = fields
+        .iter()
+        .map(|f| {
+            let name = &f.name;
+            let marker = &f.marker;
+            quote::quote!(pub(crate) #name: crate::properties::Property<'a, #marker>)
+        })
+        .collect::<Vec<proc_macro2::TokenStream>>();
+
+    let pub_struct_decl = quote::quote!(pub struct #public_name<'a> {
+        #(#public_field_decls),*
+    });
+
+    
+    unreachable!()
+}
diff --git a/crates/synthizer_macros_internal/src/utils.rs b/crates/synthizer_macros_internal/src/utils.rs
new file mode 100644
index 0000000..7c72782
--- /dev/null
+++ b/crates/synthizer_macros_internal/src/utils.rs
@@ -0,0 +1,61 @@
+/// Given an identifier an some code, wrap the code in a "sealed" module:
+///
+/// ```IGNORE
+/// mod xxx_sealed {
+///     use super::*;
+///     tokens here...
+/// }
+///
+/// pub(crate) use xxx_sealed::*;
+/// ```
+///
+/// The sealed module name is derived from the identifier by converting it to snake case and adding _sealed.
+pub(crate) fn seal<T: quote::ToTokens>(ident: &syn::Ident, tokens: &T) -> proc_macro2::TokenStream {
+    let cased = ident_case::RenameRule::SnakeCase.apply_to_field(ident.to_string());
+    let mod_token: syn::Ident = syn::parse_quote!(#cased);
+    quote::quote!(
+        mod #mod_token {
+            use super::*;
+
+            #tokens
+        }
+
+        pub(crate) use sealed::*;
+    )
+}
+
+/// Builds a match statement like this:
+///
+/// ```IGNORE
+/// match index {
+///     0 => expr0,
+/// 1 => expr1,
+/// ...
+/// _ => panic!("Index out of bounds"),
+/// }
+/// ```
+///
+/// This is used to allow turning user-supplied indices into references to fields on heterogeneous types, primarily
+/// method calls, where we can't use arrays without overhead. This shows up in e.g. property slots, where propertis of
+/// different types have different concrete representations.
+fn build_indexing_match<I: Iterator<Item = impl quote::ToTokens>>(
+    index: syn::Expr,
+    items: I,
+) -> syn::ExprMatch {
+    let arms = items
+        .enumerate()
+        .map(|(index, expr)| quote::quote!(#index => #expr))
+        .collect::<Vec<_>>();
+    let arm_count = arms.len();
+    let index_error = if arm_count > 0 {
+        format!("Index {{}} must not be over {}", arm_count - 1)
+    } else {
+        "Got index {}, but no indices are accepted here; this is expected to be dead code"
+            .to_string()
+    };
+
+    syn::parse_quote!(match #index {
+        #(#arms),*
+        _ => panic!(#index_error, #index),
+    })
+}