fix the doc

datafusion/sql/src/unparser/mod.rs

@@ -116,7 +116,11 @@ impl<'a> Unparser<'a> {
     /// Implementation of [`UserDefinedLogicalNodeUnparser`] can be added to the root unparser to handle custom logical nodes.
     ///
     /// The child unparsers are called iteratively.
-    /// see [Unparser::extension_to_sql] and [Unparser::extension_to_statement] for more details.
+    /// There are two methods in [`Unparser`] will be called:
+    /// - `extension_to_statement`: This method is called when the custom logical node is a custom statement.
+    ///     If multiple child unparsers return a non-None value, the last unparsing result will be returned.
+    /// - `extension_to_sql`: This method is called when the custom logical node is part of a statement.
+    ///    If multiple child unparsers are registered for the same custom logical node, all of them will be called in order.
     pub fn with_udlp_unparsers(
         mut self,
         udlp_unparsers: Vec<Arc<dyn UserDefinedLogicalNodeUnparser>>,