diff --git a/ci/before_deploy.sh b/ci/before_deploy.sh
index 4f1b75b7..25fa14e0 100755
--- a/ci/before_deploy.sh
+++ b/ci/before_deploy.sh
@@ -29,11 +29,15 @@ cd "$pkg"
 strip "$strip_option" "$name/bin/cquery" "$name/${libclang[-1]}"
 case $(uname -s) in
   Darwin)
+    # https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/tar.1.html
+    # macOS's bsdtar is lack of flags to set uid/gid.
+    # First, we generate a list of file in mtree format.
     tar -cf filelist --format=mtree --options="!all,time,mode,type" "$name"
+    # Then add a line "/set uid=0 gid=0" after the first line "#mtree".
     awk '/#mtree/{print;print "/set uid=0 gid=0";next}1' filelist > newflielist
+    # Finally, use the list to generate the tarball.
     tar -zcf "$root/build/$name.tar.gz" @newflielist ;;
   Linux)
-    # ./bin/cquery -> $name/bin/cquery
     tar -Jcf "$root/build/$name.tar.xz" --owner 0 --group 0 $name ;;
   *)
     tar -Jcf "$root/build/$name.tar.xz" --uid 0 --gid 0 $name ;;