Unfortunately there is no record of important or written by Apple in this update. All just around the system bug fixes to improve stability and performance of the operating system.
Apple also accelerate the schedule for OS X El Capitan Developer Beta 6 release a few days ago. The same was done on OS X Yosemite.
Apple introduced OS X El Capitan in Yosemite successor WWDC 2015 event a few months ago. Until now there are two versions of OS X El Capitan beta is for developers and general users registered in the Apple Beta Software Program. While the public version will be available late autumn of this year around October 2015.
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