Usage
srcset="$url1 500w, $url0"
srcset="$url1 300w, $url0"
srcset="$url1 500w, $url2 300w, $url0"
srcset="$url1 500w, $url2 300w, $url3 2x, $url0"
srcset="$url1 500w 2x, $url2 300w, $url3 2x, $url0"
srcset="$url1 500w, $url2 300w, $url3 400h, $url0"
srcset="$url1 500w 2x, $url2 300w, $url3 400h, $url0"
srcset="$url1 500w 2x, $url2 300w, $url3 400h, $url0"
srcset="$url1 500w 2x, $url2 300w, $url3 400h, $url0"
srcset="$url1 500w 2x, $url2 300w, $url3 400h, $url0"
srcset="$url1 500w 2x, $url2 300w 200h, $url3 400h 500w, $url0"
srcset="$url1 500w 2x, $url2 300w 200h, $url3 400h 500w, $url0"
srcset="$url1 500w 2x, $url2 300w 200h, $url3 400h 500w, $url0"
srcset="$url1 500w 2x, $url2 300w 200h, $url3 400h 500w, $url0"
srcset="$url1 500w 2x, $url2 300w 200h, $url3 400h 500w, $url0"
srcset="$url1 500w 2x, $url2 300w 900h, $url3 800w 200h, $url0"
srcset="$url1 500w 2x, $url2 300w 900h, $url3 800w 200h, $url0"
srcset="$url1 500w 2x, $url2 300w 900h, $url3 800w 200h, $url0"
Example
<img srcset="thumbnail-400h.png 1480w, thumbnail-800h.png 2x, thumbnail-200h.png">