Taking into account additional property names but not comparing their values.

src/wasm/additional_property.rs

@@ -0,0 +1,27 @@
+use std::collections::HashMap;
+
+use serde::Serialize;
+
+use super::WasmAstNode;
+
+#[derive(Debug, Serialize)]
+pub enum AdditionalPropertyValue<'s, 'p> {
+    SingleString(&'s str),
+    ListOfStrings(Vec<&'s str>),
+    OptionalPair {
+        optval: Option<&'s str>,
+        val: &'s str,
+    },
+    ObjectTree(Vec<(Option<Vec<WasmAstNode<'s, 'p>>>, Vec<WasmAstNode<'s, 'p>>)>),
+}
+
+#[derive(Debug, Serialize, Default)]
+pub struct AdditionalProperties<'s, 'p> {
+    pub(crate) properties: HashMap<String, AdditionalPropertyValue<'s, 'p>>,
+}
+
+impl<'s, 'p> AdditionalProperties<'s, 'p> {
+    pub(crate) fn get_elisp_names<'c>(&'c self) -> impl Iterator<Item = String> + 'c {
+        self.properties.keys().map(move |key| format!(":{}", key))
+    }
+}