Backwards compatibility is a cornerstone of the WordPress core development philosophy. It is, unfortunately, not something nearly enough plugin or theme developers take seriously. When a plugin or theme project gains 10s or 100s of thousands of users, backwards compatibility can be crucial to the overall health of the project.
In this session, Pippin shares how backwards compatibility is a foundational belief within the WordPress community and the WordPress platform tries very hard not to break things between upgrades. Ensuring backwards compatibility is more of a mental mindset than anything. Developers have to mentally make the commitment and say to themselves “I will NOT break installs during upgrades”.