'main': Add a comment.

Author: danielshahaf

highlighters/main/main-highlighter.zsh

@@ -988,6 +988,7 @@ _zsh_highlight_main_highlighter_check_path()
   # Search the path in CDPATH
   if [[ $expanded_path != /* ]]; then
     local cdpath_dir
+    # TODO: When we've dropped support for pre-5.0.6 zsh, use the *(Y1) glob qualifier here.
     for cdpath_dir in $cdpath ; do
       [[ -e "$cdpath_dir/$expanded_path" ]] && return 0
     done