diff --git a/src/main.rs b/src/main.rs
index 520ceb0..3399308 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,9 +13,11 @@ fn main() {
     let matches = args::get_args_matches();
     let parsed_args = args::parse_args(matches);
 
+    // read plist file
     let plist_value = Value::from_file(&parsed_args.in_file).unwrap_or_else(|e| {
         failure_and_exit!("Read plist file: {}, failed: {}", parsed_args.in_file, e);
     });
+    // write plist to file or stdout
     if let Some(out_file) = parsed_args.out_file {
         if File::open(&out_file).is_ok() {
             failure_and_exit!("Output file exits: {}", out_file);