What heuristics do browsers use to cache resources not explicitly set to be cachable?

Question

13.2.2 Heuristic Expiration

Since origin servers do not always provide explicit expiration times, HTTP caches typically assign heuristic

Answer 1

Seems like webkit ("...the OS X system framework version of the engine that's used by Safari...") uses the same heuristics as Chromium.

The following is taken from CacheValidation.cpp:

return (creationTime - lastModifiedValue) * 0.1;