diff --git a/compiler/erg_parser/parse.rs b/compiler/erg_parser/parse.rs
index 1ddc3dbd..0d36eb47 100644
--- a/compiler/erg_parser/parse.rs
+++ b/compiler/erg_parser/parse.rs
@@ -68,11 +68,13 @@ pub enum ArrayInner {
     },
 }
 
+/// Perform recursive descent parsing.
+///
 /// To enhance error descriptions, the parsing process will continue as long as it's not fatal.
 #[derive(Debug)]
 pub struct Parser {
     counter: DefId,
-    level: usize,
+    level: usize, // nest level (for debugging)
     tokens: TokenStream,
     warns: ParseErrors,
     errs: ParseErrors,