Thanks D.O.
I chose SEARCH_PLACEHOLDER as it seems commonly used.
I'm not sure if to use that javascript technique.
If you browse with js diabled you have to delete the characters in the search box.
I suppose anyone that wants it that way can simply put a modified function (renaming it to e.g. nm_search_js in the theme's functions.php and call it in the template.
Edit: I've added a new function nm_search_with_placeholder to NM Addons (0.6)
I chose SEARCH_PLACEHOLDER as it seems commonly used.
I'm not sure if to use that javascript technique.
If you browse with js diabled you have to delete the characters in the search box.
I suppose anyone that wants it that way can simply put a modified function (renaming it to e.g. nm_search_js in the theme's functions.php and call it in the template.
Edit: I've added a new function nm_search_with_placeholder to NM Addons (0.6)