Make more of Markup...
…and other small features you must not miss
Split View of one app
Although Apple describes Split View as being a way to put two apps side by side with an appearance similar to full-screen mode, this new feature doesn’t restrict you to showing two different apps; you can put two windows from the same app side by side. This is useful with Finder when archiving contents from your Mac’s internal storage to another drive, to look at two revisions of a Pages document together, or to refer to a copy of a Numbers spreadsheet to look up and type cell references in the master.
You have a greater degree of control over the presentation of any annotations you add to images or PDFs in Preview or using the Markup tool in Mail – provided your Mac has a trackpad. Select all or just some of your annotations and then twist two fingers on the trackpad’s surface to rotate them through 360 degrees. There are no shortcuts to snap to multiples of 90 degrees, but this should make it easier for you to squeeze notes into margins so they can be printed.
AirPlay from QuickTime
HTML5 video in Safari isn’t the only kind of video that can be streamed to Apple TV using AirPlay. This capability is also available in QuickTime Player 10, so any video you can open in that app can be streamed over your network to a very large screen. With a file open in QuickTime, look for the familiar AirPlay icon towards the right-hand side of the playback controls. Click it to see a list of AirPlay video receivers on your network, then click the name of one of them to start broadcasting to it.