With WordPress 4.1 came my first contribution to Core! Woot woot!
View the 4.1 release notes here
While playing with the Twenty Fifteen theme a development website, I happened to notice that one set of conditions resulted in HTML being rendered to screen rather than properly evaluated as HTML markup. A quick Trac ticket and a patch later, and my change was accepted into the 4.1 release cycle!
Obviously a very minor change, but an important one that needed to be made before the new Twenty Fifteen theme could/should be released along with WordPress 4.1. Looking forward to making more contribution efforts – and hopefully larger ones – to Core in the future!