diff --git a/types/src/number/mod.rs b/types/src/number/mod.rs
index 665e86f..f09d06a 100644
--- a/types/src/number/mod.rs
+++ b/types/src/number/mod.rs
@@ -22,6 +22,7 @@ type Int = i64;
 type Flt = f64;
 
 trait Number: Debug + IsBool + IsChar + IsNumber + Value {
+    /// Convert a Number to the next lowest type in Scheme's number pyramid, if possible.
     fn convert_down(&self) -> Option<Box<Number>>;
 }