Weird "sizes" and "srcset" attribute when using the_post_thumbnail
Created by: numeroteca
The code:
the_post_thumbnail( 'medium', array('class' => 'img-responsive') );
generates an image like:
<img src="http://globalrec.org/wp-content/uploads/2015/07/demands-from-wps-500x317.jpg" class="img-responsive wp-post-image" alt="demands from wps" srcset="http://globalrec.org/wp-content/uploads/2015/07/demands-from-wps-500x317.jpg 500w, http://globalrec.org/wp-content/uploads/2015/07/demands-from-wps-1024x649.jpg 1024w" sizes="(max-width: 500px) 100vw, 500px" height="317" width="500">
See it live:
http://globalrec.org/creating-a-newsletter/
Does it have to do with new responsive features?