One of macOS’s unsung features is the ability to install extensions. These are add-on features—plug-ins—that expand what your Mac can do. Each is associated with a full-blown program you’ve installed on your Mac; they can come from Apple or anybody else. This System Preferences panel lists the ones you’ve got installed so far, and lets you turn off the ones you don’t use.
Extensions (Figure 10-16) can modify four parts of the Mac:
Actions, Photos. You probably have only one item in each of these items, called Markup. That’s Apple’s own extension, and it lets you mark up attachments in Mail, TextEdit, Photos, and some other programs. In theory, these extensions do something to whatever text or graphics you’ve selected.
Finder. These features operate on files at the desktop. The most common example is Dropbox; its extension adds Dropbox commands (like Share Dropbox Link) to the shortcut menu when you right-click or two-finger click an icon in your Dropbox folder, and adds a green checkmark icon to each file that’s been synced with Dropbox online. (Google Drive works similarly.)
Share Menu. You know the Share button that appears all across macOS (Notes on Disk Swapping)? It produces a list of different ways (Mail, Messages, or Facebook) that you can share whatever you’ve got selected (a map, a web page, a photo). Well, that list is extensible. Your programs can insert their own sharing options into it.
Today. The Today pane of the Notification Center is described in Today Tab—but what’s fascinating is that you can now install new information chunks (widgets, as Apple calls them) to that display. Everybody can choose from the starter widgets like Calculator, Calendar, and Weather—but other programs can install additional info-bits here.
Each of these extension categories works in the same way, as shown in Figure 10-16.
