Image dialog

I'm trying to understand the two responsive text boxes in the image properties pop-up.  Assuming it's related to display on mobile devices but how do I make use of those?

 

Hi,

This is very advanced functionality that comes from CKEditor, which is the WYSIWYG editor we use. There's no way to upload multiple versions of images in attachments from the Composr UI, but if you're willing to hand-upload files and hand-craft the settings here, then the syntax is described here…

Responsive Images - The srcset and sizes Attributes | bitsofcode

Thanks for the link....that clears that one up.