When you're customizing the behavior of your app, you can create your own, but there are also a number of system actions. These are actions that are automatically created by the AppSheet system based on the column structure of a table. System actions represent the default behavior of an AppSheet app; you can think of them as behavior that comes with the app out of the box.
The most common example of system actions are per-column system actions. Every column of type Email has an automatically-created Email system action. This is shown as an email envelope icon next to any email address value shown in an app view. Clicking on it launches an email to that email address. Similarly, any lat-long value has a map pin icon next to it. Clicking on the icon opens a map and shows the location of that value on the map.
Controlling System Actions
In most apps, there is no reason to ever modify or control the system actions. They are designed to work correctly without the app creator's intervention.
However, there are instances where the app creator may want to control these actions. For example, perhaps the app should not enable calling certain phone numbers, or change the icon shown for email actions, etc. There is an option on the editor's action pane to "Show System Actions". Once the system actions are shown, they can be edited like any other action. However, there are some caveats:
Only some of the properties of the action can be changed --- in particular, the presentation properties and the condition that determines when it should be shown.
If the table's column structure changes, the system will automatically delete and re-create system actions. Any changes made by the app creator will be lost if the system deletes the action.
Hiding System Actions
In some cases, you may want to hide the system action icons from your user to provide a cleaner look to your app. In that case, you can select any of the system actions and choose the "Do not display" option. This means that the action is still there if you want to bring it back, but won't be displayed from the user. This way you can show the user only the icons they need.