1. The repo for the boilerplate is: https://github.com/MozaikAgency/wp-theme-bootstrap
2. The helper mentioned: https://github.com/MozaikAgency/wp-theme-bootstrap/blob/mast...
3. Code demoing how the helper would be used: https://github.com/MozaikAgency/wp-theme-bootstrap/blob/ccdf...
4. Resp images polyfill - PictureFill: https://github.com/scottjehl/picturefill
5. lazy-loading content js lib - lazySizes: https://github.com/aFarkas/lazysizes
6. object-fit polyfill - Object-fit: https://github.com/anselmh/object-fit
7. Vote for object-fit to be included in IE: https://wpdev.uservoice.com/forums/257854-microsoft-edge-dev...