The behavior of require and *data-readers* was modified in Clojure 1.7.0 to look for files ending with .cljc as well as files ending with .clj, but their doc strings do not mention this change.
Patch: clj-1873-v1.patch
Screened by: Alex Miller
Patch clj-1873-v1.patch dated Jan 1 2016 adds mentions of .cljc files to the doc strings of require and *data-readers*