Selectors are one of the major configuration elements and can be used in a rule to provide issue(s) for further processing.

• You can add one or multiple selectors to a rule depending on the trigger type of the rule. 
• You can add multiple conditions, actions, nested conditions, and their corresponding actions to the selector.
• Any issues returned by the selector will be processed according to those conditions and actions that are added directly to that selector.
• Even though you can add multiple selectors to a rule, you cannot add a selector to a selector.

Think of a selector as a "Do while there are issues" loop. The automation rule iteratively processes each issue returned by the selector and performs an action on each of the issues.

The options actually available depend on which other elements (triggers and/or selectors) have been selected upfront.