explain how convert creates some files in current directory

product/ERP5/Document/Image.py

@@ -334,6 +334,8 @@ class Image(TextConvertableMixin, File, OFSImage):
       parameter_list.append('-')
 
     if format:
+      # png:- will write on stdout after converting to png
+      # xxxpng:- will write to a file named xxxpng:- in current directory
       parameter_list.append('%s:-' % format)
     else:
       parameter_list.append('-')