Add commas between allowed file extensions I need to restrict the user to upload only the file extensions that i mentioned in the Allowed file extensions filed. It works properly. But in front-end, i need to add a comma separator for this format.

Actual - Allowed file types: ai aif avi bmp csv doc docx eps fla flv gif img.

Expected - Allowed file types: ai, aif, avi, bmp, csv, doc, docx, eps, fla, flv, gif, img
You are definitely allowed to separate file types by comma in the admin are



For user area, find the ID of the form (you can find this in the firebug) then 

function YourTheme_form_alter(&amp;$form, &amp;$form_state, $form_id){
      if($form_id == "TheFormID"){
            kpr($form);  
      }
}


In this way you can find the form elements. get the Key of image field in the form array, if it is image then write

function YourTheme_form_alter(&amp;$form, &amp;$form_state, $form_id){
      if($form_id == "TheFormID"){
            $form['image']['#description'] = t('File types are comma separated')
      }
}


This is the general idea but a few modification might be needed