diff --git a/implementations/rust/Cargo.toml b/implementations/rust/Cargo.toml
index d7bd888..95980e3 100644
--- a/implementations/rust/Cargo.toml
+++ b/implementations/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "preserves"
-version = "0.2.3"
+version = "0.3.0"
 authors = ["Tony Garnock-Jones <tonyg@leastfixedpoint.com>"]
 edition = "2018"
 description = "Implementation of the Preserves serialization format via serde."
diff --git a/implementations/rust/src/lib.rs b/implementations/rust/src/lib.rs
index 1b63b94..acc9c43 100644
--- a/implementations/rust/src/lib.rs
+++ b/implementations/rust/src/lib.rs
@@ -1,13 +1,17 @@
 pub mod value;
 pub mod symbol;
 
+#[cfg(test)]
+type Dom = ();
+
 #[cfg(test)]
 mod ieee754_section_5_10_total_order_tests {
     use std::cmp::Ordering::{Less, Equal, Greater};
+    use super::Dom;
 
     use crate::value::{Value, PlainValue};
-    fn f(val: f32) -> Value<PlainValue> { Value::from(val) }
-    fn d(val: f64) -> Value<PlainValue> { Value::from(val) }
+    fn f(val: f32) -> Value<PlainValue<Dom>, Dom> { Value::from(val) }
+    fn d(val: f64) -> Value<PlainValue<Dom>, Dom> { Value::from(val) }
 
     // TODO: Test cases with a few different signalling and non-signalling NaNs
 
@@ -99,8 +103,9 @@ mod ieee754_section_5_10_total_order_tests {
 mod value_tests {
     use crate::value::{Value, PlainValue};
     use num::bigint::BigInt;
+    use super::Dom;
 
-    type VV = Value<PlainValue>;
+    type VV = Value<PlainValue<Dom>, Dom>;
 
     #[test] fn boolean_mut() {
         let mut b = VV::Boolean(true);
@@ -179,10 +184,11 @@ mod value_tests {
 mod decoder_tests {
     use crate::value::Decoder;
     use crate::value::{Value, PlainValue, NestedValue};
+    use super::Dom;
 
     #[test] fn read_123() {
         let mut buf = &b"abc"[..];
-        let mut d = Decoder::<_, PlainValue>::new(&mut buf, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut buf, None);
         assert_eq!(d.read().ok(), Some(97));
         assert_eq!(d.read().ok(), Some(98));
         assert_eq!(d.read().ok(), Some(99));
@@ -191,7 +197,7 @@ mod decoder_tests {
 
     #[test] fn skip_annotations_noskip() {
         let mut buf = &b"\x0521"[..];
-        let mut d = Decoder::<_, PlainValue>::new(&mut buf, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut buf, None);
         let v = d.next().unwrap();
         assert_eq!(v.annotations().len(), 1);
         assert_eq!(v.annotations()[0], Value::from(2).wrap());
@@ -200,7 +206,7 @@ mod decoder_tests {
 
     #[test] fn skip_annotations_skip() {
         let mut buf = &b"\x0521"[..];
-        let mut d = Decoder::<_, PlainValue>::new(&mut buf, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut buf, None);
         d.set_read_annotations(false);
         let v = d.next().unwrap();
         assert_eq!(v.annotations().len(), 0);
@@ -210,7 +216,7 @@ mod decoder_tests {
     #[test] fn two_values_at_once() {
         let mut buf = &b"\x81tPing\x81tPong"[..];
         assert_eq!(buf.len(), 12);
-        let mut d = Decoder::<_, PlainValue>::new(&mut buf, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut buf, None);
         assert_eq!(d.next().unwrap().value(), &Value::simple_record("Ping", vec![]));
         assert_eq!(d.next().unwrap().value(), &Value::simple_record("Pong", vec![]));
         assert_eq!(buf.len(), 0);
@@ -219,7 +225,7 @@ mod decoder_tests {
     #[test] fn buf_advanced() {
         let mut buf = &b"\x81tPing\x81tPong"[..];
         assert_eq!(buf.len(), 12);
-        let mut d = Decoder::<_, PlainValue>::new(&mut buf, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut buf, None);
         assert_eq!(d.next().unwrap().value(), &Value::simple_record("Ping", vec![]));
         assert_eq!(buf.len(), 6);
     }
@@ -233,9 +239,10 @@ mod samples_tests {
     use crate::value::DecodePlaceholderMap;
     use crate::value::to_value;
     use crate::value::from_value;
+    use super::Dom;
 
     #[derive(Debug, serde::Serialize, serde::Deserialize)]
-    struct ExpectedPlaceholderMapping(DecodePlaceholderMap<PlainValue>);
+    struct ExpectedPlaceholderMapping(DecodePlaceholderMap<PlainValue<Dom>, Dom>);
 
     #[derive(Debug, serde::Serialize, serde::Deserialize)]
     struct TestCases {
@@ -245,9 +252,9 @@ mod samples_tests {
 
     #[derive(Debug, serde::Serialize, serde::Deserialize)]
     enum TestCase {
-        Test(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue),
-        NondeterministicTest(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue),
-        StreamingTest(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue),
+        Test(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue<Dom>),
+        NondeterministicTest(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue<Dom>),
+        StreamingTest(#[serde(with = "serde_bytes")] Vec<u8>, PlainValue<Dom>),
         ParseError(String),
         ParseShort(String),
         DecodeError(#[serde(with = "serde_bytes")] Vec<u8>),
@@ -256,7 +263,7 @@ mod samples_tests {
 
     #[test] fn run() -> std::io::Result<()> {
         let mut fh = std::fs::File::open("../../tests/samples.bin").unwrap();
-        let mut d = Decoder::<_, PlainValue>::new(&mut fh, None);
+        let mut d = Decoder::<_, PlainValue<Dom>, Dom>::new(&mut fh, None);
         let tests: TestCases = from_value(&d.next().unwrap()).unwrap();
         // println!("{:#?}", tests);
 
@@ -312,7 +319,7 @@ mod samples_tests {
                                #[serde(with = "serde_bytes")] &'a [u8],
                                #[serde(with = "serde_bytes")] Vec<u8>,
                                i16,
-                               PlainValue);
+                               PlainValue<Dom>);
         let v = SimpleValue("hello".to_string(),
                             "sym1".to_string(),
                             Symbol("sym2".to_string()),
@@ -322,7 +329,7 @@ mod samples_tests {
                             12345,
                             Value::from("hi").wrap());
         println!("{:#?}", v);
-        let w: PlainValue = to_value(&v).unwrap();
+        let w: PlainValue<Dom> = to_value(&v).unwrap();
         println!("{:#?}", w);
         let x = from_value(&w).unwrap();
         println!("{:#?}", &x);
diff --git a/implementations/rust/src/symbol.rs b/implementations/rust/src/symbol.rs
index f2e2b63..fb6b4ac 100644
--- a/implementations/rust/src/symbol.rs
+++ b/implementations/rust/src/symbol.rs
@@ -5,13 +5,13 @@ pub struct Symbol(pub String);
 
 impl serde::Serialize for Symbol {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: serde::Serializer {
-        Value::<PlainValue>::symbol(&self.0).wrap().serialize(serializer)
+        Value::<PlainValue<()>, ()>::symbol(&self.0).wrap().serialize(serializer)
     }
 }
 
 impl<'de> serde::Deserialize<'de> for Symbol {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: serde::Deserializer<'de> {
-        let v = PlainValue::deserialize(deserializer)?;
+        let v = PlainValue::<()>::deserialize(deserializer)?;
         let s = v.value().as_symbol().ok_or_else(|| serde::de::Error::custom("Expected symbol"))?;
         Ok(Symbol(s.clone()))
     }
diff --git a/implementations/rust/src/value/codec.rs b/implementations/rust/src/value/codec.rs
index bb5d39e..55d5ac9 100644
--- a/implementations/rust/src/value/codec.rs
+++ b/implementations/rust/src/value/codec.rs
@@ -1,15 +1,15 @@
-use crate::value::{decoder, encoder, invert_map, NestedValue};
+use crate::value::{decoder, encoder, invert_map, NestedValue, Domain};
 use decoder::{Decoder, DecodePlaceholderMap};
 use encoder::{Encoder, EncodePlaceholderMap};
 use std::io::{Read, Write};
 
-pub struct Codec<N: NestedValue> {
-    pub decode_placeholders: Option<DecodePlaceholderMap<N>>,
-    pub encode_placeholders: Option<EncodePlaceholderMap<N>>,
+pub struct Codec<N: NestedValue<D>, D: Domain> {
+    pub decode_placeholders: Option<DecodePlaceholderMap<N, D>>,
+    pub encode_placeholders: Option<EncodePlaceholderMap<N, D>>,
 }
 
-impl<N: NestedValue> Codec<N> {
-    pub fn new(decode_placeholders: DecodePlaceholderMap<N>) -> Self {
+impl<N: NestedValue<D>, D: Domain> Codec<N, D> {
+    pub fn new(decode_placeholders: DecodePlaceholderMap<N, D>) -> Self {
         let encode_placeholders = Some(invert_map(&decode_placeholders));
         Codec { decode_placeholders: Some(decode_placeholders), encode_placeholders }
     }
@@ -18,11 +18,11 @@ impl<N: NestedValue> Codec<N> {
         Codec { decode_placeholders: None, encode_placeholders: None }
     }
 
-    pub fn decoder<'a, 'r, R: Read>(&'a self, read: &'r mut R) -> Decoder<'r, 'a, R, N> {
+    pub fn decoder<'a, 'r, R: Read>(&'a self, read: &'r mut R) -> Decoder<'r, 'a, R, N, D> {
         Decoder::new(read, self.decode_placeholders.as_ref())
     }
 
-    pub fn encoder<'a, 'w, W: Write>(&'a self, write: &'w mut W) -> Encoder<'w, 'a, W, N> {
+    pub fn encoder<'a, 'w, W: Write>(&'a self, write: &'w mut W) -> Encoder<'w, 'a, W, N, D> {
         Encoder::new(write, self.encode_placeholders.as_ref())
     }
 
diff --git a/implementations/rust/src/value/de.rs b/implementations/rust/src/value/de.rs
index 9d6e266..22db7d9 100644
--- a/implementations/rust/src/value/de.rs
+++ b/implementations/rust/src/value/de.rs
@@ -1,4 +1,4 @@
-use crate::value::{Value, NestedValue, Map};
+use crate::value::{Value, NestedValue, Map, Domain};
 use crate::value::value::{Float, Double};
 use crate::value::error::{Error, Result, ExpectedKind};
 use num::traits::cast::ToPrimitive;
@@ -6,33 +6,39 @@ use serde::Deserialize;
 use serde::de::{Visitor, SeqAccess, MapAccess, EnumAccess, VariantAccess, DeserializeSeed};
 use std::convert::TryFrom;
 use std::iter::Iterator;
+use std::marker::PhantomData;
 
-pub struct Deserializer<'de, N: NestedValue> {
+pub struct Deserializer<'de, N: NestedValue<D>, D: Domain> {
     input: &'de N,
+    phantom: PhantomData<D>,
 }
 
-pub fn from_value<'a, T, N: NestedValue>(v: &'a N) -> Result<T> where T: Deserialize<'a> {
+pub fn from_value<'a, T, N: NestedValue<D>, D: 'a + Domain>(v: &'a N) ->
+    Result<T, D> where T: Deserialize<'a>
+{
     let mut de = Deserializer::from_value(v);
     let t = T::deserialize(&mut de)?;
     Ok(t)
 }
 
-impl<'de, N: NestedValue> Deserializer<'de, N> {
+impl<'de, N: NestedValue<D>, D: 'de + Domain> Deserializer<'de, N, D> {
     pub fn from_value(v: &'de N) -> Self {
-        Deserializer{ input: v }
+        Deserializer{ input: v, phantom: PhantomData }
     }
 
-    fn check<'a, T, F>(&'a mut self, f: F, k: ExpectedKind) -> Result<T>
-    where F: FnOnce(&'de Value<N>) -> Option<T>
+    fn check<'a, T, F>(&'a mut self, f: F, k: ExpectedKind) -> Result<T, D>
+    where F: FnOnce(&'de Value<N, D>) -> Option<T>
     {
         f(self.input.value()).ok_or_else(|| Error::Expected(k, self.input.copy_via()))
     }
 }
 
-impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deserializer<'de, N> {
-    type Error = Error;
+impl<'de, 'a, N: NestedValue<D>, D: 'de + Domain> serde::de::Deserializer<'de>
+    for &'a mut Deserializer<'de, N, D>
+{
+    type Error = Error<D>;
 
-    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let v = self.input.value();
         match v {
@@ -67,70 +73,70 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
         }
     }
 
-    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_bool(self.check(|v| v.as_boolean(), ExpectedKind::Boolean)?)
     }
 
-    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_i8(i.to_i8().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_i16(i.to_i16().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_i32(i.to_i32().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_i64(i.to_i64().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_u8(i.to_u8().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_u16(i.to_u16().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_u32(i.to_u32().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let i = self.check(|v| v.as_signedinteger(), ExpectedKind::SignedInteger)?;
         visitor.visit_u64(i.to_u64().ok_or_else(|| Error::NumberTooLarge(i.clone()))?)
     }
 
-    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_f32(self.check(|v| v.as_float(), ExpectedKind::Float)?)
     }
 
-    fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_f64(self.check(|v| v.as_double(), ExpectedKind::Double)?)
     }
 
-    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let fs = self.check(|v| v.as_simple_record("UnicodeScalar", Some(1)),
                             ExpectedKind::SimpleRecord("UnicodeScalar", Some(1)))?;
@@ -139,27 +145,27 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
         visitor.visit_char(char::try_from(c).or(Err(Error::InvalidUnicodeScalar(c)))?)
     }
 
-    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_borrowed_str(&self.check(|v| v.as_string(), ExpectedKind::String)?)
     }
 
-    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         self.deserialize_str(visitor)
     }
 
-    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_borrowed_bytes(&self.check(|v| v.as_bytestring(), ExpectedKind::ByteString)?)
     }
 
-    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_byte_buf(self.check(|v| v.as_bytestring(), ExpectedKind::ByteString)?.clone())
     }
 
-    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         match self.input.value().as_simple_record("None", Some(0)) {
             Some(_fs) => visitor.visit_none(),
@@ -173,7 +179,7 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
         }
     }
 
-    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         if self.input.value().is_simple_record("tuple", Some(0)) {
             visitor.visit_unit()
@@ -183,7 +189,7 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
     }
 
     fn deserialize_unit_struct<V>(self, name: &'static str, visitor: V)
-                                  -> Result<V::Value> where V: Visitor<'de>
+                                  -> Result<V::Value, D> where V: Visitor<'de>
     {
         if self.input.value().is_simple_record(name, Some(0)) {
             visitor.visit_unit()
@@ -193,7 +199,7 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
     }
 
     fn deserialize_newtype_struct<V>(self, name: &'static str, visitor: V)
-                                     -> Result<V::Value> where V: Visitor<'de>
+                                     -> Result<V::Value, D> where V: Visitor<'de>
     {
         if name == crate::value::value::MAGIC {
             let mut buf: Vec<u8> = Vec::new();
@@ -208,12 +214,12 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
         }
     }
 
-    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de> {
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de> {
         let vs = self.check(|v| v.as_sequence(), ExpectedKind::Sequence)?;
         visitor.visit_seq(VecSeq::new(self, vs))
     }
 
-    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_tuple<V>(self, len: usize, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         let fs = self.check(|v| v.as_simple_record("tuple", Some(len)),
                             ExpectedKind::SimpleRecord("tuple", Some(len)))?;
@@ -221,14 +227,14 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
     }
 
     fn deserialize_tuple_struct<V>(self, name: &'static str, len: usize, visitor: V)
-                                   -> Result<V::Value> where V: Visitor<'de>
+                                   -> Result<V::Value, D> where V: Visitor<'de>
     {
         let fs = self.check(|v| v.as_simple_record(name, Some(len)),
                             ExpectedKind::SimpleRecord(name, Some(len)))?;
         visitor.visit_seq(VecSeq::new(self, fs))
     }
 
-    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de> {
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de> {
         let d = self.check(|v| v.as_dictionary(), ExpectedKind::Dictionary)?;
         visitor.visit_map(DictMap::new(self, d))
     }
@@ -237,7 +243,7 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
                              name: &'static str,
                              fields: &'static [&'static str],
                              visitor: V)
-                             -> Result<V::Value> where V: Visitor<'de>
+                             -> Result<V::Value, D> where V: Visitor<'de>
     {
         let fs = self.check(|v| v.as_simple_record(name, Some(fields.len())),
                             ExpectedKind::SimpleRecord(name, Some(fields.len())))?;
@@ -248,39 +254,39 @@ impl<'de, 'a, N: NestedValue> serde::de::Deserializer<'de> for &'a mut Deseriali
                            _name: &'static str,
                            _variants: &'static [&'static str],
                            visitor: V)
-                           -> Result<V::Value> where V: Visitor<'de>
+                           -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_enum(self)
     }
 
-    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_borrowed_str(&self.check(|v| v.as_symbol(), ExpectedKind::Symbol)?)
     }
 
-    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value> where V: Visitor<'de>
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_none()
     }
 }
 
-pub struct VecSeq<'a, 'de: 'a, N: NestedValue> {
+pub struct VecSeq<'a, 'de: 'a, N: NestedValue<D>, D: Domain> {
     index: usize,
     vec: &'de [N],
-    de: &'a mut Deserializer<'de, N>,
+    de: &'a mut Deserializer<'de, N, D>,
 }
 
-impl<'de, 'a, N: NestedValue> VecSeq<'a, 'de, N> {
-    fn new(de: &'a mut Deserializer<'de, N>, vec: &'de [N]) -> Self {
+impl<'de, 'a, N: NestedValue<D>, D: Domain> VecSeq<'a, 'de, N, D> {
+    fn new(de: &'a mut Deserializer<'de, N, D>, vec: &'de [N]) -> Self {
         VecSeq{ index: 0, vec, de }
     }
 }
 
-impl<'de, 'a, N: NestedValue> SeqAccess<'de> for VecSeq<'a, 'de, N> {
-    type Error = Error;
+impl<'de, 'a, N: NestedValue<D>, D: 'de + Domain> SeqAccess<'de> for VecSeq<'a, 'de, N, D> {
+    type Error = Error<D>;
 
     fn next_element_seed<T>(&mut self, seed: T)
-                            -> Result<Option<T::Value>> where T: DeserializeSeed<'de>
+                            -> Result<Option<T::Value>, D> where T: DeserializeSeed<'de>
     {
         if self.index == self.vec.len() {
             return Ok(None)
@@ -293,23 +299,23 @@ impl<'de, 'a, N: NestedValue> SeqAccess<'de> for VecSeq<'a, 'de, N> {
     }
 }
 
-pub struct DictMap<'a, 'de: 'a, N: NestedValue> {
+pub struct DictMap<'a, 'de: 'a, N: NestedValue<D>, D: Domain> {
     pending: Option<&'de N>,
     iter: Box<dyn Iterator<Item = (&'de N, &'de N)> + 'a>,
-    de: &'a mut Deserializer<'de, N>,
+    de: &'a mut Deserializer<'de, N, D>,
 }
 
-impl<'de, 'a, N: NestedValue> DictMap<'a, 'de, N> {
-    fn new(de: &'a mut Deserializer<'de, N>, d: &'de Map<N, N>) -> Self {
+impl<'de, 'a, N: NestedValue<D>, D: Domain> DictMap<'a, 'de, N, D> {
+    fn new(de: &'a mut Deserializer<'de, N, D>, d: &'de Map<N, N>) -> Self {
         DictMap{ pending: None, iter: Box::new(d.iter()), de }
     }
 }
 
-impl<'de, 'a, N: NestedValue> MapAccess<'de> for DictMap<'a, 'de, N> {
-    type Error = Error;
+impl<'de, 'a, N: NestedValue<D>, D: 'de + Domain> MapAccess<'de> for DictMap<'a, 'de, N, D> {
+    type Error = Error<D>;
 
     fn next_key_seed<K>(&mut self, seed: K)
-                        -> Result<Option<K::Value>> where K: DeserializeSeed<'de>
+                        -> Result<Option<K::Value>, D> where K: DeserializeSeed<'de>
     {
         match self.iter.next() {
             None => Ok(None),
@@ -321,7 +327,7 @@ impl<'de, 'a, N: NestedValue> MapAccess<'de> for DictMap<'a, 'de, N> {
         }
     }
 
-    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value> where V: DeserializeSeed<'de> {
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, D> where V: DeserializeSeed<'de> {
         let v = self.pending.unwrap();
         self.pending = None;
         self.de.input = v;
@@ -329,12 +335,12 @@ impl<'de, 'a, N: NestedValue> MapAccess<'de> for DictMap<'a, 'de, N> {
     }
 }
 
-impl<'a, 'de, N: NestedValue> EnumAccess<'de> for &'a mut Deserializer<'de, N> {
-    type Error = Error;
+impl<'a, 'de, N: NestedValue<D>, D: 'de + Domain> EnumAccess<'de> for &'a mut Deserializer<'de, N, D> {
+    type Error = Error<D>;
     type Variant = Self;
 
     fn variant_seed<V>(self, seed: V)
-                       -> Result<(V::Value, Self::Variant)> where V: DeserializeSeed<'de>
+                       -> Result<(V::Value, Self::Variant), D> where V: DeserializeSeed<'de>
     {
         let (lp, _) = self.check(|v| v.as_record(), ExpectedKind::Record)?;
         let v = self.input;
@@ -345,25 +351,25 @@ impl<'a, 'de, N: NestedValue> EnumAccess<'de> for &'a mut Deserializer<'de, N> {
     }
 }
 
-impl<'a, 'de, N: NestedValue> VariantAccess<'de> for &'a mut Deserializer<'de, N> {
-    type Error = Error;
+impl<'a, 'de, N: NestedValue<D>, D: 'de + Domain> VariantAccess<'de> for &'a mut Deserializer<'de, N, D> {
+    type Error = Error<D>;
 
-    fn unit_variant(self) -> Result<()> {
+    fn unit_variant(self) -> Result<(), D> {
         Ok(())
     }
 
-    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value> where T: DeserializeSeed<'de> {
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, D> where T: DeserializeSeed<'de> {
         let (_, fs) = self.input.value().as_record().unwrap();
         self.input = &fs[0];
         seed.deserialize(&mut *self)
     }
 
-    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value> where V: Visitor<'de> {
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, D> where V: Visitor<'de> {
         visitor.visit_seq(VecSeq::new(self, &self.input.value().as_record().unwrap().1))
     }
 
     fn struct_variant<V>(self, _fields: &'static [&'static str], visitor: V)
-                         -> Result<V::Value> where V: Visitor<'de>
+                         -> Result<V::Value, D> where V: Visitor<'de>
     {
         visitor.visit_seq(VecSeq::new(self, &self.input.value().as_record().unwrap().1))
     }
diff --git a/implementations/rust/src/value/decoder.rs b/implementations/rust/src/value/decoder.rs
index 35dbc05..e76e96a 100644
--- a/implementations/rust/src/value/decoder.rs
+++ b/implementations/rust/src/value/decoder.rs
@@ -1,7 +1,7 @@
 use std::io::{Read, ErrorKind};
 use std::convert::TryInto;
 use std::convert::TryFrom;
-use crate::value::{Value, NestedValue, Set, Map};
+use crate::value::{Value, NestedValue, Set, Map, Domain};
 use num::bigint::BigInt;
 use crate::value::constants::{Op, InvalidOp, AtomMinor, CompoundMinor};
 
@@ -48,7 +48,7 @@ impl Error {
     pub fn is_eof(&self) -> bool { if let Error::Eof = *self { true } else { false } }
 }
 
-pub type DecodePlaceholderMap<N> = Map<usize, Value<N>>;
+pub type DecodePlaceholderMap<N, D> = Map<usize, Value<N, D>>;
 
 #[derive(PartialEq, Eq)]
 enum PeekState {
@@ -57,11 +57,11 @@ enum PeekState {
     Full(u8),
 }
 
-pub struct Decoder<'a, 'b, R: Read, N: NestedValue> {
+pub struct Decoder<'a, 'b, R: Read, N: NestedValue<D>, D: Domain> {
     read: &'a mut R,
     index: usize,
     buf: Box<PeekState>,
-    placeholders: Option<&'b DecodePlaceholderMap<N>>,
+    placeholders: Option<&'b DecodePlaceholderMap<N, D>>,
     read_annotations: bool,
 }
 
@@ -69,8 +69,8 @@ fn decodeint(bs: &[u8]) -> BigInt {
     BigInt::from_signed_bytes_be(bs)
 }
 
-impl<'a, 'b, R: Read, N: NestedValue> Decoder<'a, 'b, R, N> {
-    pub fn new(read: &'a mut R, placeholders: Option<&'b DecodePlaceholderMap<N>>) -> Self {
+impl<'a, 'b, R: Read, N: NestedValue<D>, D: Domain> Decoder<'a, 'b, R, N, D> {
+    pub fn new(read: &'a mut R, placeholders: Option<&'b DecodePlaceholderMap<N, D>>) -> Self {
         Decoder{
             read,
             index: 0,
@@ -190,7 +190,7 @@ impl<'a, 'b, R: Read, N: NestedValue> Decoder<'a, 'b, R, N> {
         Ok(match minor {
             AtomMinor::SignedInteger => Value::from(decodeint(&bs)).wrap(),
             AtomMinor::String => Value::from(std::str::from_utf8(&bs)?).wrap(),
-            AtomMinor::ByteString => Value::from(bs).wrap(),
+            AtomMinor::ByteString => Value::from(&bs as &[u8]).wrap(),
             AtomMinor::Symbol => Value::symbol(std::str::from_utf8(&bs)?).wrap(),
         })
     }
diff --git a/implementations/rust/src/value/encoder.rs b/implementations/rust/src/value/encoder.rs
index a629ac0..bb12aae 100644
--- a/implementations/rust/src/value/encoder.rs
+++ b/implementations/rust/src/value/encoder.rs
@@ -1,5 +1,5 @@
 use std::io::Write;
-use crate::value::value::{Value, NestedValue, Float, Double, Map};
+use crate::value::value::{Value, NestedValue, Float, Double, Map, Domain};
 use num::bigint::BigInt;
 use num::cast::ToPrimitive;
 use crate::value::constants::{Op, AtomMinor, CompoundMinor};
@@ -7,15 +7,15 @@ use crate::value::constants::{Op, AtomMinor, CompoundMinor};
 pub type Error = std::io::Error;
 pub type Result = std::result::Result<(), Error>;
 
-pub type EncodePlaceholderMap<N> = Map<Value<N>, usize>;
+pub type EncodePlaceholderMap<N, D> = Map<Value<N, D>, usize>;
 
-pub struct Encoder<'a, 'b, W: Write, N: NestedValue> {
+pub struct Encoder<'a, 'b, W: Write, N: NestedValue<D>, D: Domain> {
     write: &'a mut W,
-    placeholders: Option<&'b EncodePlaceholderMap<N>>,
+    placeholders: Option<&'b EncodePlaceholderMap<N, D>>,
 }
 
-impl<'a, 'b, W: Write, N: NestedValue> Encoder<'a, 'b, W, N> {
-    pub fn new(write: &'a mut W, placeholders: Option<&'b EncodePlaceholderMap<N>>) -> Self {
+impl<'a, 'b, W: Write, N: NestedValue<D>, D: Domain> Encoder<'a, 'b, W, N, D> {
+    pub fn new(write: &'a mut W, placeholders: Option<&'b EncodePlaceholderMap<N, D>>) -> Self {
         Encoder{ write, placeholders }
     }
 
@@ -78,7 +78,7 @@ impl<'a, 'b, W: Write, N: NestedValue> Encoder<'a, 'b, W, N> {
         self.write_value(v.value())
     }
 
-    pub fn write_value(&mut self, v: &Value<N>) -> Result {
+    pub fn write_value(&mut self, v: &Value<N, D>) -> Result {
         match self.placeholders.and_then(|m| m.get(v)) {
             Some(&n) => self.write_header(Op::Misc(1), n),
             None => match v {
@@ -117,6 +117,10 @@ impl<'a, 'b, W: Write, N: NestedValue> Encoder<'a, 'b, W, N> {
                     for (k, v) in vs { self.write(k)?; self.write(v)?; }
                     Ok(())
                 }
+                Value::Domain(ref d) =>
+                    Err(Error::new(std::io::ErrorKind::InvalidData,
+                                   format!("Cannot Preserves-encode domain-specific value {:?}",
+                                           d))),
             }
         }
     }
diff --git a/implementations/rust/src/value/error.rs b/implementations/rust/src/value/error.rs
index a88bce3..f13a67e 100644
--- a/implementations/rust/src/value/error.rs
+++ b/implementations/rust/src/value/error.rs
@@ -1,13 +1,13 @@
 use num::bigint::BigInt;
-use crate::value::PlainValue;
+use crate::value::{PlainValue, Domain};
 
 #[derive(Debug)]
-pub enum Error {
+pub enum Error<D: Domain> {
     Message(String),
     InvalidUnicodeScalar(u32),
     NumberTooLarge(BigInt),
     CannotDeserializeAny,
-    Expected(ExpectedKind, PlainValue),
+    Expected(ExpectedKind, PlainValue<D>),
     InternalMagicError,
 }
 
@@ -29,23 +29,23 @@ pub enum ExpectedKind {
     Dictionary,
 }
 
-pub type Result<T> = std::result::Result<T, Error>;
+pub type Result<T, D> = std::result::Result<T, Error<D>>;
 
-impl serde::ser::Error for Error {
+impl<D: Domain> serde::ser::Error for Error<D> {
     fn custom<T: std::fmt::Display>(msg: T) -> Self {
         Self::Message(msg.to_string())
     }
 }
 
-impl serde::de::Error for Error {
+impl<D: Domain> serde::de::Error for Error<D> {
     fn custom<T: std::fmt::Display>(msg: T) -> Self {
         Self::Message(msg.to_string())
     }
 }
 
-impl std::error::Error for Error {}
+impl<D: Domain> std::error::Error for Error<D> {}
 
-impl std::fmt::Display for Error {
+impl<D: Domain> std::fmt::Display for Error<D> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(f, "{:?}", self)
     }
diff --git a/implementations/rust/src/value/mod.rs b/implementations/rust/src/value/mod.rs
index e04548b..cd65c31 100644
--- a/implementations/rust/src/value/mod.rs
+++ b/implementations/rust/src/value/mod.rs
@@ -16,6 +16,7 @@ pub use encoder::EncodePlaceholderMap;
 pub use encoder::Encoder;
 pub use ser::Serializer;
 pub use ser::to_value;
+pub use value::Domain;
 pub use value::NestedValue;
 pub use value::Value;
 pub use value::AnnotatedValue;
diff --git a/implementations/rust/src/value/ser.rs b/implementations/rust/src/value/ser.rs
index c9853d0..d9be201 100644
--- a/implementations/rust/src/value/ser.rs
+++ b/implementations/rust/src/value/ser.rs
@@ -1,106 +1,109 @@
-use crate::value::{Value, NestedValue, Map};
+use crate::value::{Value, NestedValue, Map, Domain};
 use serde::Serialize;
 use crate::value::error::{Error, Result};
 use std::marker::PhantomData;
 
-pub struct Serializer<N: NestedValue> {
-    phantom: PhantomData<N>
+pub struct Serializer<N: NestedValue<D>, D: Domain> {
+    phantom: PhantomData<(N, D)>,
 }
 
-pub struct SerializeDictionary<N: NestedValue> {
+pub struct SerializeDictionary<N: NestedValue<D>, D: Domain> {
     next_key: Option<N>,
     items: Map<N,N>,
+    phantom: PhantomData<D>,
 }
 
-pub struct SerializeRecord<N: NestedValue> {
+pub struct SerializeRecord<N: NestedValue<D>, D: Domain> {
     name: &'static str,
     vec: Vec<N>,
+    phantom: PhantomData<D>,
 }
 
-pub struct SerializeSequence<N: NestedValue> {
+pub struct SerializeSequence<N: NestedValue<D>, D: Domain> {
     vec: Vec<N>,
+    phantom: PhantomData<D>,
 }
 
-impl<N: NestedValue> serde::Serializer for Serializer<N> {
+impl<N: NestedValue<D>, D: Domain> serde::Serializer for Serializer<N, D> {
     type Ok = N;
-    type Error = Error;
-    type SerializeSeq = SerializeSequence<N>;
-    type SerializeTuple = SerializeRecord<N>;
-    type SerializeTupleStruct = SerializeRecord<N>;
-    type SerializeTupleVariant = SerializeRecord<N>;
-    type SerializeMap = SerializeDictionary<N>;
-    type SerializeStruct = SerializeRecord<N>;
-    type SerializeStructVariant = SerializeRecord<N>;
+    type Error = Error<D>;
+    type SerializeSeq = SerializeSequence<N, D>;
+    type SerializeTuple = SerializeRecord<N, D>;
+    type SerializeTupleStruct = SerializeRecord<N, D>;
+    type SerializeTupleVariant = SerializeRecord<N, D>;
+    type SerializeMap = SerializeDictionary<N, D>;
+    type SerializeStruct = SerializeRecord<N, D>;
+    type SerializeStructVariant = SerializeRecord<N, D>;
 
-    fn serialize_bool(self, v: bool) -> Result<Self::Ok> {
+    fn serialize_bool(self, v: bool) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_i8(self, v: i8) -> Result<Self::Ok> {
+    fn serialize_i8(self, v: i8) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_i16(self, v: i16) -> Result<Self::Ok> {
+    fn serialize_i16(self, v: i16) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_i32(self, v: i32) -> Result<Self::Ok> {
+    fn serialize_i32(self, v: i32) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_i64(self, v: i64) -> Result<Self::Ok> {
+    fn serialize_i64(self, v: i64) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_u8(self, v: u8) -> Result<Self::Ok> {
+    fn serialize_u8(self, v: u8) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_u16(self, v: u16) -> Result<Self::Ok> {
+    fn serialize_u16(self, v: u16) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_u32(self, v: u32) -> Result<Self::Ok> {
+    fn serialize_u32(self, v: u32) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_u64(self, v: u64) -> Result<Self::Ok> {
+    fn serialize_u64(self, v: u64) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_f32(self, v: f32) -> Result<Self::Ok> {
+    fn serialize_f32(self, v: f32) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_f64(self, v: f64) -> Result<Self::Ok> {
+    fn serialize_f64(self, v: f64) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_char(self, v: char) -> Result<Self::Ok> {
+    fn serialize_char(self, v: char) -> Result<Self::Ok, D> {
         Ok(Value::simple_record("UnicodeScalar", vec![Value::from(v as u32).wrap()]).wrap())
     }
 
-    fn serialize_str(self, v: &str) -> Result<Self::Ok> {
+    fn serialize_str(self, v: &str) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok> {
+    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, D> {
         Ok(Value::from(v).wrap())
     }
 
-    fn serialize_none(self) -> Result<Self::Ok> {
+    fn serialize_none(self) -> Result<Self::Ok, D> {
         Ok(Value::simple_record("None", vec![]).wrap())
     }
 
-    fn serialize_some<T: ?Sized>(self, v: &T) -> Result<Self::Ok> where T: Serialize {
+    fn serialize_some<T: ?Sized>(self, v: &T) -> Result<Self::Ok, D> where T: Serialize {
         Ok(Value::simple_record("Some", vec![to_value(v)?]).wrap())
     }
 
-    fn serialize_unit(self) -> Result<Self::Ok> {
+    fn serialize_unit(self) -> Result<Self::Ok, D> {
         Ok(Value::simple_record("tuple", vec![]).wrap())
     }
 
-    fn serialize_unit_struct(self, name: &'static str) -> Result<Self::Ok> {
+    fn serialize_unit_struct(self, name: &'static str) -> Result<Self::Ok, D> {
         Ok(Value::simple_record(name, vec![]).wrap())
     }
 
@@ -108,16 +111,16 @@ impl<N: NestedValue> serde::Serializer for Serializer<N> {
                               _name: &'static str,
                               _variant: u32,
                               variant_name: &'static str) ->
-        Result<Self::Ok>
+        Result<Self::Ok, D>
     {
         Ok(Value::simple_record(variant_name, vec![]).wrap())
     }
 
     fn serialize_newtype_struct<T: ?Sized>(self, name: &'static str, value: &T) ->
-        Result<Self::Ok> where T: Serialize
+        Result<Self::Ok, D> where T: Serialize
     {
         if name == crate::value::value::MAGIC {
-            let v: crate::value::PlainValue = to_value(value)?;
+            let v: crate::value::PlainValue<D> = to_value(value)?;
             let mut buf: &[u8] = v.value().as_bytestring().ok_or(Error::InternalMagicError)?;
             crate::value::Decoder::new(&mut buf, None).next().or(Err(Error::InternalMagicError))
         } else {
@@ -131,24 +134,24 @@ impl<N: NestedValue> serde::Serializer for Serializer<N> {
                                             _variant: u32,
                                             variant_name: &'static str,
                                             value: &T) ->
-        Result<Self::Ok> where T: Serialize
+        Result<Self::Ok, D> where T: Serialize
     {
         Ok(Value::simple_record(variant_name, vec![to_value(value)?]).wrap())
     }
 
-    fn serialize_seq(self, count: Option<usize>) -> Result<Self::SerializeSeq> {
+    fn serialize_seq(self, count: Option<usize>) -> Result<Self::SerializeSeq, D> {
         let vec = match count { Some(n) => Vec::with_capacity(n), None => Vec::new() };
-        Ok(SerializeSequence{ vec })
+        Ok(SerializeSequence{ vec, phantom: PhantomData })
     }
 
-    fn serialize_tuple(self, count: usize) -> Result<Self::SerializeTuple> {
-        Ok(SerializeRecord{ name: "tuple", vec: Vec::with_capacity(count) })
+    fn serialize_tuple(self, count: usize) -> Result<Self::SerializeTuple, D> {
+        Ok(SerializeRecord{ name: "tuple", vec: Vec::with_capacity(count), phantom: PhantomData })
     }
 
     fn serialize_tuple_struct(self, name: &'static str, count: usize) ->
-        Result<Self::SerializeTupleStruct>
+        Result<Self::SerializeTupleStruct, D>
     {
-        Ok(SerializeRecord{ name, vec: Vec::with_capacity(count) })
+        Ok(SerializeRecord{ name, vec: Vec::with_capacity(count), phantom: PhantomData })
     }
 
     fn serialize_tuple_variant(self,
@@ -156,17 +159,17 @@ impl<N: NestedValue> serde::Serializer for Serializer<N> {
                                _variant: u32,
                                variant_name: &'static str,
                                count: usize) ->
-        Result<Self::SerializeTupleVariant>
+        Result<Self::SerializeTupleVariant, D>
     {
-        Ok(SerializeRecord{ name: variant_name, vec: Vec::with_capacity(count) })
+        Ok(SerializeRecord{ name: variant_name, vec: Vec::with_capacity(count), phantom: PhantomData })
     }
 
-    fn serialize_map(self, _count: Option<usize>) -> Result<Self::SerializeMap> {
-        Ok(SerializeDictionary{ next_key: None, items: Map::new() })
+    fn serialize_map(self, _count: Option<usize>) -> Result<Self::SerializeMap, D> {
+        Ok(SerializeDictionary{ next_key: None, items: Map::new(), phantom: PhantomData })
     }
 
-    fn serialize_struct(self, name: &'static str, count: usize) -> Result<Self::SerializeStruct> {
-        Ok(SerializeRecord{ name, vec: Vec::with_capacity(count) })
+    fn serialize_struct(self, name: &'static str, count: usize) -> Result<Self::SerializeStruct, D> {
+        Ok(SerializeRecord{ name, vec: Vec::with_capacity(count), phantom: PhantomData })
     }
 
     fn serialize_struct_variant(self,
@@ -174,126 +177,126 @@ impl<N: NestedValue> serde::Serializer for Serializer<N> {
                                 _variant: u32,
                                 variant_name: &'static str,
                                 count: usize) ->
-        Result<Self::SerializeStructVariant>
+        Result<Self::SerializeStructVariant, D>
     {
-        Ok(SerializeRecord{ name: variant_name, vec: Vec::with_capacity(count) })
+        Ok(SerializeRecord{ name: variant_name, vec: Vec::with_capacity(count), phantom: PhantomData })
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeMap for SerializeDictionary<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeMap for SerializeDictionary<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<()> where T: Serialize {
+    fn serialize_key<T: ?Sized>(&mut self, key: &T) -> Result<(), D> where T: Serialize {
         self.next_key = Some(to_value(key)?);
         Ok(())
     }
 
-    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<()> where T: Serialize {
+    fn serialize_value<T: ?Sized>(&mut self, value: &T) -> Result<(), D> where T: Serialize {
         let key = self.next_key.take().unwrap();
         self.items.insert(key, to_value(value)?);
         Ok(())
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         Ok(Value::from(self.items).wrap())
     }
 }
 
-impl<N: NestedValue> SerializeRecord<N> {
-    fn push(&mut self, value: N) -> Result<()> {
+impl<N: NestedValue<D>, D: Domain> SerializeRecord<N, D> {
+    fn push(&mut self, value: N) -> Result<(), D> {
         self.vec.push(value);
         Ok(())
     }
 
-    fn finish(self) -> Result<N> {
+    fn finish(self) -> Result<N, D> {
         Ok(Value::simple_record(self.name, self.vec).wrap())
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeStruct for SerializeRecord<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeStruct for SerializeRecord<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_field<T: ?Sized>(&mut self, _name: &'static str, value: &T) -> Result<()>
+    fn serialize_field<T: ?Sized>(&mut self, _name: &'static str, value: &T) -> Result<(), D>
     where T: Serialize
     {
         self.push(to_value(value)?)
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         self.finish()
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeStructVariant for SerializeRecord<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeStructVariant for SerializeRecord<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_field<T: ?Sized>(&mut self, _name: &'static str, value: &T) -> Result<()>
+    fn serialize_field<T: ?Sized>(&mut self, _name: &'static str, value: &T) -> Result<(), D>
     where T: Serialize
     {
         self.push(to_value(value)?)
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         self.finish()
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeTuple for SerializeRecord<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeTuple for SerializeRecord<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<()> where T: Serialize {
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), D> where T: Serialize {
         self.push(to_value(value)?)
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         self.finish()
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeTupleStruct for SerializeRecord<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeTupleStruct for SerializeRecord<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<()> where T: Serialize {
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), D> where T: Serialize {
         self.push(to_value(value)?)
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         self.finish()
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeTupleVariant for SerializeRecord<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeTupleVariant for SerializeRecord<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<()> where T: Serialize {
+    fn serialize_field<T: ?Sized>(&mut self, value: &T) -> Result<(), D> where T: Serialize {
         self.push(to_value(value)?)
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         self.finish()
     }
 }
 
-impl<N: NestedValue> serde::ser::SerializeSeq for SerializeSequence<N> {
+impl<N: NestedValue<D>, D: Domain> serde::ser::SerializeSeq for SerializeSequence<N, D> {
     type Ok = N;
-    type Error = Error;
+    type Error = Error<D>;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<()> where T: Serialize {
+    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), D> where T: Serialize {
         self.vec.push(to_value(value)?);
         Ok(())
     }
 
-    fn end(self) -> Result<Self::Ok> {
+    fn end(self) -> Result<Self::Ok, D> {
         Ok(Value::from(self.vec).wrap())
     }
 }
 
-pub fn to_value<T, N>(value: T) -> Result<N> where T: Serialize, N: NestedValue {
+pub fn to_value<T, N, D: Domain>(value: T) -> Result<N, D> where T: Serialize, N: NestedValue<D> {
     value.serialize(Serializer{ phantom: PhantomData })
 }
diff --git a/implementations/rust/src/value/value.rs b/implementations/rust/src/value/value.rs
index 78755bd..d100c4c 100644
--- a/implementations/rust/src/value/value.rs
+++ b/implementations/rust/src/value/value.rs
@@ -11,18 +11,20 @@ use num::traits::cast::ToPrimitive;
 pub use std::collections::BTreeSet as Set;
 pub use std::collections::BTreeMap as Map;
 
-pub trait NestedValue: Sized + Debug + Clone + Eq + Hash + Ord {
+pub trait Domain: Sized + Debug + Clone + Eq + Hash + Ord {}
+
+pub trait NestedValue<D: Domain>: Sized + Debug + Clone + Eq + Hash + Ord {
     type BoxType: Sized + Debug + Clone + Eq + Hash + Ord;
 
-    fn wrap(v: Value<Self>) -> Self;
-    fn wrap_ann(anns: Vec<Self>, v: Value<Self>) -> Self;
+    fn wrap(v: Value<Self, D>) -> Self;
+    fn wrap_ann(anns: Vec<Self>, v: Value<Self, D>) -> Self;
 
     fn boxwrap(self) -> Self::BoxType;
     fn boxunwrap(b: &Self::BoxType) -> &Self;
 
     fn annotations(&self) -> &[Self];
-    fn value(&self) -> &Value<Self>;
-    fn value_owned(self) -> Value<Self>;
+    fn value(&self) -> &Value<Self, D>;
+    fn value_owned(self) -> Value<Self, D>;
 
     fn debug_fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         for ann in self.annotations() {
@@ -31,7 +33,7 @@ pub trait NestedValue: Sized + Debug + Clone + Eq + Hash + Ord {
         self.value().fmt(f)
     }
 
-    fn copy_via<M: NestedValue>(&self) -> M {
+    fn copy_via<M: NestedValue<D>>(&self) -> M {
         M::wrap_ann(self.annotations().iter().map(|a| a.copy_via()).collect(),
                     self.value().copy_via())
     }
@@ -39,7 +41,7 @@ pub trait NestedValue: Sized + Debug + Clone + Eq + Hash + Ord {
 
 /// The `Value`s from the specification.
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub enum Value<N> where N: NestedValue {
+pub enum Value<N, D> where N: NestedValue<D>, D: Domain {
     Boolean(bool),
     Float(Float),
     Double(Double),
@@ -47,10 +49,11 @@ pub enum Value<N> where N: NestedValue {
     String(String),
     ByteString(Vec<u8>),
     Symbol(String),
-    Record(Record<N>),
+    Record(Record<N, D>),
     Sequence(Vec<N>),
     Set(Set<N>),
     Dictionary(Map<N, N>),
+    Domain(D),
 }
 
 /// Single-precision IEEE 754 Value
@@ -62,7 +65,7 @@ pub struct Float(pub f32);
 pub struct Double(pub f64);
 
 /// A Record `Value`
-pub type Record<N> = (<N as NestedValue>::BoxType, Vec<N>);
+pub type Record<N, D> = (<N as NestedValue<D>>::BoxType, Vec<N>);
 
 impl From<f32> for Float {
     fn from(v: f32) -> Self {
@@ -148,34 +151,34 @@ impl PartialOrd for Double {
 
 impl Eq for Double {}
 
-impl<N: NestedValue> From<bool> for Value<N> { fn from(v: bool) -> Self { Value::Boolean(v) } }
+impl<N: NestedValue<D>, D: Domain> From<bool> for Value<N, D> { fn from(v: bool) -> Self { Value::Boolean(v) } }
 
-impl<N: NestedValue> From<f32> for Value<N> { fn from(v: f32) -> Self { Value::Float(Float::from(v)) } }
-impl<N: NestedValue> From<f64> for Value<N> { fn from(v: f64) -> Self { Value::Double(Double::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<f32> for Value<N, D> { fn from(v: f32) -> Self { Value::Float(Float::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<f64> for Value<N, D> { fn from(v: f64) -> Self { Value::Double(Double::from(v)) } }
 
-impl<N: NestedValue> From<u8> for Value<N> { fn from(v: u8) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<i8> for Value<N> { fn from(v: i8) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<u16> for Value<N> { fn from(v: u16) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<i16> for Value<N> { fn from(v: i16) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<u32> for Value<N> { fn from(v: u32) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<i32> for Value<N> { fn from(v: i32) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<u64> for Value<N> { fn from(v: u64) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<i64> for Value<N> { fn from(v: i64) -> Self { Value::from(i128::from(v)) } }
-impl<N: NestedValue> From<u128> for Value<N> { fn from(v: u128) -> Self { Value::SignedInteger(BigInt::from(v)) } }
-impl<N: NestedValue> From<i128> for Value<N> { fn from(v: i128) -> Self { Value::SignedInteger(BigInt::from(v)) } }
-impl<N: NestedValue> From<BigInt> for Value<N> { fn from(v: BigInt) -> Self { Value::SignedInteger(v) } }
+impl<N: NestedValue<D>, D: Domain> From<u8> for Value<N, D> { fn from(v: u8) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<i8> for Value<N, D> { fn from(v: i8) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<u16> for Value<N, D> { fn from(v: u16) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<i16> for Value<N, D> { fn from(v: i16) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<u32> for Value<N, D> { fn from(v: u32) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<i32> for Value<N, D> { fn from(v: i32) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<u64> for Value<N, D> { fn from(v: u64) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<i64> for Value<N, D> { fn from(v: i64) -> Self { Value::from(i128::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<u128> for Value<N, D> { fn from(v: u128) -> Self { Value::SignedInteger(BigInt::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<i128> for Value<N, D> { fn from(v: i128) -> Self { Value::SignedInteger(BigInt::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<BigInt> for Value<N, D> { fn from(v: BigInt) -> Self { Value::SignedInteger(v) } }
 
-impl<N: NestedValue> From<&str> for Value<N> { fn from(v: &str) -> Self { Value::String(String::from(v)) } }
-impl<N: NestedValue> From<String> for Value<N> { fn from(v: String) -> Self { Value::String(v) } }
+impl<N: NestedValue<D>, D: Domain> From<&str> for Value<N, D> { fn from(v: &str) -> Self { Value::String(String::from(v)) } }
+impl<N: NestedValue<D>, D: Domain> From<String> for Value<N, D> { fn from(v: String) -> Self { Value::String(v) } }
 
-impl<N: NestedValue> From<&[u8]> for Value<N> { fn from(v: &[u8]) -> Self { Value::ByteString(Vec::from(v)) } }
-impl<N: NestedValue> From<Vec<u8>> for Value<N> { fn from(v: Vec<u8>) -> Self { Value::ByteString(v) } }
+impl<N: NestedValue<D>, D: Domain> From<&[u8]> for Value<N, D> { fn from(v: &[u8]) -> Self { Value::ByteString(Vec::from(v)) } }
+// impl<N: NestedValue<D>, D: Domain> From<Vec<u8>> for Value<N, D> { fn from(v: Vec<u8>) -> Self { Value::ByteString(v) } }
 
-impl<N: NestedValue> From<Vec<N>> for Value<N> { fn from(v: Vec<N>) -> Self { Value::Sequence(v) } }
-impl<N: NestedValue> From<Set<N>> for Value<N> { fn from(v: Set<N>) -> Self { Value::Set(v) } }
-impl<N: NestedValue> From<Map<N, N>> for Value<N> { fn from(v: Map<N, N>) -> Self { Value::Dictionary(v) } }
+impl<N: NestedValue<D>, D: Domain> From<Vec<N>> for Value<N, D> { fn from(v: Vec<N>) -> Self { Value::Sequence(v) } }
+impl<N: NestedValue<D>, D: Domain> From<Set<N>> for Value<N, D> { fn from(v: Set<N>) -> Self { Value::Set(v) } }
+impl<N: NestedValue<D>, D: Domain> From<Map<N, N>> for Value<N, D> { fn from(v: Map<N, N>) -> Self { Value::Dictionary(v) } }
 
-impl<N: NestedValue> Debug for Value<N> {
+impl<N: NestedValue<D>, D: Domain> Debug for Value<N, D> {
     // Not *quite* a formatter for the Preserves text syntax, since it
     // doesn't escape strings/symbols properly.
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
@@ -213,14 +216,15 @@ impl<N: NestedValue> Debug for Value<N> {
                 f.write_str("#set")?;
                 f.debug_set().entries(v.iter()).finish()
             }
-            Value::Dictionary(ref v) => f.debug_map().entries(v.iter()).finish()
+            Value::Dictionary(ref v) => f.debug_map().entries(v.iter()).finish(),
+            Value::Domain(ref d) => write!(f, "{:?}", d),
         }
     }
 }
 
 //---------------------------------------------------------------------------
 
-impl<N: NestedValue> Value<N> {
+impl<N: NestedValue<D>, D: Domain> Value<N, D> {
     pub fn wrap(self) -> N {
         N::wrap(self)
     }
@@ -354,7 +358,7 @@ impl<N: NestedValue> Value<N> {
         }
     }
 
-    pub fn symbol(s: &str) -> Value<N> {
+    pub fn symbol(s: &str) -> Value<N, D> {
         Value::Symbol(s.to_string())
     }
 
@@ -378,7 +382,7 @@ impl<N: NestedValue> Value<N> {
         }
     }
 
-    pub fn record(label: N, fields: Vec<N>) -> Value<N> {
+    pub fn record(label: N, fields: Vec<N>) -> Value<N, D> {
         Value::Record((label.boxwrap(), fields))
     }
 
@@ -386,7 +390,7 @@ impl<N: NestedValue> Value<N> {
         self.as_record().is_some()
     }
 
-    pub fn as_record(&self) -> Option<&Record<N>> {
+    pub fn as_record(&self) -> Option<&Record<N, D>> {
         if let Value::Record(ref r) = *self {
             Some(r)
         } else {
@@ -394,7 +398,7 @@ impl<N: NestedValue> Value<N> {
         }
     }
 
-    pub fn as_record_mut(&mut self) -> Option<&mut Record<N>> {
+    pub fn as_record_mut(&mut self) -> Option<&mut Record<N, D>> {
         if let Value::Record(ref mut r) = *self {
             Some(r)
         } else {
@@ -402,7 +406,7 @@ impl<N: NestedValue> Value<N> {
         }
     }
 
-    pub fn simple_record(label: &str, fields: Vec<N>) -> Value<N> {
+    pub fn simple_record(label: &str, fields: Vec<N>) -> Value<N, D> {
         Value::record(Value::symbol(label).wrap(), fields)
     }
 
@@ -484,7 +488,7 @@ impl<N: NestedValue> Value<N> {
         }
     }
 
-    pub fn copy_via<M: NestedValue>(&self) -> Value<M> {
+    pub fn copy_via<M: NestedValue<D>>(&self) -> Value<M, D> {
         match self {
             Value::Boolean(b) => Value::Boolean(*b),
             Value::Float(f) => Value::Float(f.clone()),
@@ -499,11 +503,12 @@ impl<N: NestedValue> Value<N> {
             Value::Set(ref v) => Value::Set(v.iter().map(|a| a.copy_via()).collect()),
             Value::Dictionary(ref v) =>
                 Value::Dictionary(v.iter().map(|(a,b)| (a.copy_via(), b.copy_via())).collect()),
+            Value::Domain(d) => Value::Domain(d.clone()),
         }
     }
 }
 
-impl<N: NestedValue> Index<usize> for Value<N> {
+impl<N: NestedValue<D>, D: Domain> Index<usize> for Value<N, D> {
     type Output = N;
 
     fn index(&self, i: usize) -> &Self::Output {
@@ -511,13 +516,13 @@ impl<N: NestedValue> Index<usize> for Value<N> {
     }
 }
 
-impl<N: NestedValue> IndexMut<usize> for Value<N> {
+impl<N: NestedValue<D>, D: Domain> IndexMut<usize> for Value<N, D> {
     fn index_mut(&mut self, i: usize) -> &mut Self::Output {
         &mut self.as_sequence_mut().unwrap()[i]
     }
 }
 
-impl<N: NestedValue> Index<&N> for Value<N> {
+impl<N: NestedValue<D>, D: Domain> Index<&N> for Value<N, D> {
     type Output = N;
 
     fn index(&self, i: &N) -> &Self::Output {
@@ -554,7 +559,7 @@ impl<'de> serde::Deserialize<'de> for ValueWrapper {
     }
 }
 
-impl<N: NestedValue> serde::Serialize for Value<N> {
+impl<N: NestedValue<D>, D: Domain> serde::Serialize for Value<N, D> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: serde::Serializer {
         let mut buf: Vec<u8> = Vec::new();
         crate::value::Encoder::new(&mut buf, None).write_value(self)
@@ -563,7 +568,7 @@ impl<N: NestedValue> serde::Serialize for Value<N> {
     }
 }
 
-impl<'de, N: NestedValue> serde::Deserialize<'de> for Value<N> {
+impl<'de, N: NestedValue<Dom>, Dom: Domain> serde::Deserialize<'de> for Value<N, Dom> {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: serde::Deserializer<'de> {
         let ValueWrapper(buf) = ValueWrapper::deserialize(deserializer)?;
         let v: N = crate::value::Decoder::new(&mut &buf[..], None).next()
@@ -572,8 +577,8 @@ impl<'de, N: NestedValue> serde::Deserialize<'de> for Value<N> {
     }
 }
 
-pub fn serialize_nested_value<S, N>(v: &N, serializer: S) ->
-    Result<S::Ok, S::Error> where S: serde::Serializer, N: NestedValue
+pub fn serialize_nested_value<S, N, D: Domain>(v: &N, serializer: S) ->
+    Result<S::Ok, S::Error> where S: serde::Serializer, N: NestedValue<D>
 {
     use serde::Serialize;
     let mut buf: Vec<u8> = Vec::new();
@@ -582,8 +587,8 @@ pub fn serialize_nested_value<S, N>(v: &N, serializer: S) ->
     ValueWrapper(buf).serialize(serializer)
 }
 
-pub fn deserialize_nested_value<'de, D, N>(deserializer: D) ->
-    Result<N, D::Error> where D: serde::Deserializer<'de>, N: NestedValue
+pub fn deserialize_nested_value<'de, D, N, Dom: Domain>(deserializer: D) ->
+    Result<N, D::Error> where D: serde::Deserializer<'de>, N: NestedValue<Dom>
 {
     use serde::Deserialize;
     let ValueWrapper(buf) = ValueWrapper::deserialize(deserializer)?;
@@ -596,29 +601,29 @@ pub fn deserialize_nested_value<'de, D, N>(deserializer: D) ->
 /// An possibly-annotated Value, with annotations (themselves
 /// possibly-annotated) in order of appearance.
 #[derive(Clone)]
-pub struct AnnotatedValue<N: NestedValue>(pub Vec<N>, pub Value<N>);
+pub struct AnnotatedValue<N: NestedValue<D>, D: Domain>(pub Vec<N>, pub Value<N, D>);
 
-impl<N: NestedValue> PartialEq for AnnotatedValue<N> {
+impl<N: NestedValue<D>, D: Domain> PartialEq for AnnotatedValue<N, D> {
     fn eq(&self, other: &Self) -> bool {
         self.1.eq(&other.1)
     }
 }
 
-impl<N: NestedValue> Eq for AnnotatedValue<N> {}
+impl<N: NestedValue<D>, D: Domain> Eq for AnnotatedValue<N, D> {}
 
-impl<N: NestedValue> Hash for AnnotatedValue<N> {
+impl<N: NestedValue<D>, D: Domain> Hash for AnnotatedValue<N, D> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.1.hash(state);
     }
 }
 
-impl<N: NestedValue> PartialOrd for AnnotatedValue<N> {
+impl<N: NestedValue<D>, D: Domain> PartialOrd for AnnotatedValue<N, D> {
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         Some(self.cmp(other))
     }
 }
 
-impl<N: NestedValue> Ord for AnnotatedValue<N> {
+impl<N: NestedValue<D>, D: Domain> Ord for AnnotatedValue<N, D> {
     fn cmp(&self, other: &Self) -> Ordering {
         self.1.cmp(&other.1)
     }
@@ -627,26 +632,26 @@ impl<N: NestedValue> Ord for AnnotatedValue<N> {
 //---------------------------------------------------------------------------
 
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct PlainValue(AnnotatedValue<PlainValue>);
+pub struct PlainValue<D: Domain>(AnnotatedValue<PlainValue<D>, D>);
 
-impl PlainValue {
+impl<D: Domain> PlainValue<D> {
     pub fn annotations_mut(&mut self) -> &mut Vec<Self> {
         &mut (self.0).0
     }
 
-    pub fn value_mut(&mut self) -> &mut Value<Self> {
+    pub fn value_mut(&mut self) -> &mut Value<Self, D> {
         &mut (self.0).1
     }
 }
 
-impl NestedValue for PlainValue {
+impl<D: Domain> NestedValue<D> for PlainValue<D> {
     type BoxType = Box<Self>;
 
-    fn wrap(v: Value<Self>) -> Self {
+    fn wrap(v: Value<Self, D>) -> Self {
         Self::wrap_ann(Vec::new(), v)
     }
 
-    fn wrap_ann(anns: Vec<Self>, v: Value<Self>) -> Self {
+    fn wrap_ann(anns: Vec<Self>, v: Value<Self, D>) -> Self {
         PlainValue(AnnotatedValue(anns, v))
     }
 
@@ -662,28 +667,28 @@ impl NestedValue for PlainValue {
         &(self.0).0
     }
 
-    fn value(&self) -> &Value<Self> {
+    fn value(&self) -> &Value<Self, D> {
         &(self.0).1
     }
 
-    fn value_owned(self) -> Value<Self> {
+    fn value_owned(self) -> Value<Self, D> {
         (self.0).1
     }
 }
 
-impl Debug for PlainValue {
+impl<D: Domain> Debug for PlainValue<D> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         self.debug_fmt(f)
     }
 }
 
-impl serde::Serialize for PlainValue {
+impl<D: Domain> serde::Serialize for PlainValue<D> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: serde::Serializer {
         serialize_nested_value(self, serializer)
     }
 }
 
-impl<'de> serde::Deserialize<'de> for PlainValue {
+impl<'de, Dom: Domain> serde::Deserialize<'de> for PlainValue<Dom> {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: serde::Deserializer<'de> {
         deserialize_nested_value(deserializer)
     }
@@ -694,16 +699,16 @@ impl<'de> serde::Deserialize<'de> for PlainValue {
 use std::rc::Rc;
 
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct RcValue(Rc<AnnotatedValue<RcValue>>);
+pub struct RcValue<D: Domain>(Rc<AnnotatedValue<RcValue<D>, D>>);
 
-impl NestedValue for RcValue {
+impl<D: Domain> NestedValue<D> for RcValue<D> {
     type BoxType = Self;
 
-    fn wrap(v: Value<Self>) -> Self {
+    fn wrap(v: Value<Self, D>) -> Self {
         Self::wrap_ann(Vec::new(), v)
     }
 
-    fn wrap_ann(anns: Vec<Self>, v: Value<Self>) -> Self {
+    fn wrap_ann(anns: Vec<Self>, v: Value<Self, D>) -> Self {
         RcValue(Rc::new(AnnotatedValue(anns, v)))
     }
 
@@ -719,28 +724,28 @@ impl NestedValue for RcValue {
         &(self.0).0
     }
 
-    fn value(&self) -> &Value<Self> {
+    fn value(&self) -> &Value<Self, D> {
         &(self.0).1
     }
 
-    fn value_owned(self) -> Value<Self> {
+    fn value_owned(self) -> Value<Self, D> {
         Rc::try_unwrap(self.0).unwrap_or_else(|_| panic!("value_owned on RcValue with refcount greater than one")).1
     }
 }
 
-impl Debug for RcValue {
+impl<D: Domain> Debug for RcValue<D> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         self.debug_fmt(f)
     }
 }
 
-impl serde::Serialize for RcValue {
+impl<D: Domain> serde::Serialize for RcValue<D> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: serde::Serializer {
         serialize_nested_value(self, serializer)
     }
 }
 
-impl<'de> serde::Deserialize<'de> for RcValue {
+impl<'de, Dom: Domain> serde::Deserialize<'de> for RcValue<Dom> {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: serde::Deserializer<'de> {
         deserialize_nested_value(deserializer)
     }
@@ -751,16 +756,16 @@ impl<'de> serde::Deserialize<'de> for RcValue {
 use std::sync::Arc;
 
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
-pub struct ArcValue(Arc<AnnotatedValue<ArcValue>>);
+pub struct ArcValue<D: Domain>(Arc<AnnotatedValue<ArcValue<D>, D>>);
 
-impl NestedValue for ArcValue {
+impl<D: Domain> NestedValue<D> for ArcValue<D> {
     type BoxType = Self;
 
-    fn wrap(v: Value<Self>) -> Self {
+    fn wrap(v: Value<Self, D>) -> Self {
         Self::wrap_ann(Vec::new(), v)
     }
 
-    fn wrap_ann(anns: Vec<Self>, v: Value<Self>) -> Self {
+    fn wrap_ann(anns: Vec<Self>, v: Value<Self, D>) -> Self {
         ArcValue(Arc::new(AnnotatedValue(anns, v)))
     }
 
@@ -776,29 +781,33 @@ impl NestedValue for ArcValue {
         &(self.0).0
     }
 
-    fn value(&self) -> &Value<Self> {
+    fn value(&self) -> &Value<Self, D> {
         &(self.0).1
     }
 
-    fn value_owned(self) -> Value<Self> {
+    fn value_owned(self) -> Value<Self, D> {
         Arc::try_unwrap(self.0).unwrap_or_else(|_| panic!("value_owned on ArcValue with refcount greater than one")).1
     }
 }
 
-impl Debug for ArcValue {
+impl<D: Domain> Debug for ArcValue<D> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         self.debug_fmt(f)
     }
 }
 
-impl serde::Serialize for ArcValue {
+impl<D: Domain> serde::Serialize for ArcValue<D> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: serde::Serializer {
         serialize_nested_value(self, serializer)
     }
 }
 
-impl<'de> serde::Deserialize<'de> for ArcValue {
+impl<'de, Dom: Domain> serde::Deserialize<'de> for ArcValue<Dom> {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: serde::Deserializer<'de> {
         deserialize_nested_value(deserializer)
     }
 }
+
+//---------------------------------------------------------------------------
+
+impl Domain for () {}