tentatively seems to be working.

src/renderer/parameters_context.rs

@@ -1,5 +1,6 @@
 use crate::parser::KVPair;
 use crate::parser::{Filter, RValue};
+use crate::renderer::context_element::CompareContextElement;
 use crate::renderer::context_element::ContextElement;
 use crate::renderer::context_element::IntoBoxedContextElement;
 use crate::renderer::walking::walk_path;
@@ -8,6 +9,7 @@ use crate::renderer::RenderError;
 use crate::renderer::Renderable;
 use crate::renderer::WalkError;
 use crate::renderer::Walkable;
+use std::any::Any;
 use std::collections::HashMap;
 
 /// Copy the data from an RValue to an Owned struct
@@ -146,3 +148,16 @@ impl IntoBoxedContextElement for String {
         Box::new(self.clone())
     }
 }
+
+impl CompareContextElement for String {
+    fn to_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn equals(&self, other: &dyn ContextElement) -> bool {
+        other
+            .to_any()
+            .downcast_ref::<Self>()
+            .map_or(false, |a| self == a)
+    }
+}