- 
        access control list 
      
- 
        X maintains a list of hosts from which client programs can be run. By
        default, only programs on the local host can use the display, plus any
        hosts specified in an initial list read by the server. This access
        control list can be changed by clients on the local host. Some
        server implementations can also implement other authorization
        mechanisms in addition to or in place of this mechanism. The action of
        this mechanism can be conditional based on the authorization protocol
        name and data received by the server at connection setup. 
      
- 
        action 
      
- 
        A function that is designed to handle an input event. CLUE input
        processing consists of matching an event with an event specification
        found in a contact's event-translations slot and then calling
        actions associated with the matching event specification. 
      
- 
        active grab 
      
- 
        A grab is active when the pointer or keyboard is actually owned
        by the single grabbing client. 
      
- 
        ancestors 
      
- 
        If W is an inferior of A, then A is an ancestor of W. 
      
- 
        atom 
      
- 
        A unique ID corresponding to a string name. Atoms are used to identify
        properties, types, and selections.