[2572] small doc update

src/lib/dns/master_lexer.h

@@ -500,9 +500,10 @@ public:
     /// hint of the progress.
     ///
     /// Note also that if a source is popped, this method will normally return
-    /// a smaller number by definition.  Likewise, the conceptual "read
-    /// cursor" would move backward after a call to \c ungetToken(), in which
-    /// case this method will return a smaller value, too.
+    /// a smaller number by definition (and so will \c getTotalSourceSize()).
+    /// Likewise, the conceptual "read cursor" would move backward after a
+    /// call to \c ungetToken(), in which case this method will return a
+    /// smaller value, too.
     ///
     /// \throw None
     size_t getPosition() const;