improve documentation in resolver code

fluent-bundle/src/resolver/pattern.rs

@@ -91,8 +91,8 @@ impl<'bundle> ResolveValue<'bundle> for ast::Pattern<&'bundle str> {
     {
         let len = self.elements.len();
 
-        // more than 1 element means concatenation, which is more efficient to write to a String
-        // 1 element often means just a message reference that can be passed back as a Cow::Borrowed
+        // If there is only 1 element, then it is more efficient to attempt to resolve as a message
+        // reference that can be passed back as a Cow::Borrowed rather than writing a new String.
         if len == 1 {
             match &self.elements[0] {
                 &ast::PatternElement::TextElement { value } => {

fluent-bundle/src/resolver/scope.rs

@@ -78,6 +78,10 @@ impl<'bundle, 'ast, 'args, 'errors, R, M> Scope<'bundle, 'ast, 'args, 'errors, R
         }
     }
 
+    /// Cyclic pattern reference detection used in expression resolvers.
+    ///
+    /// Writes an error as soon as an identical pattern is encountered more than once, 
+    /// which would lead to an infinite loop.
     pub fn track<W>(
         &mut self,
         w: &mut W,