This illustration shows the List assignees who receive the task dialog box.

The dialog box is broken into two sections. The top part contains the Build a list of participants using (drop-down list with the value of Names and Expressions).

Below that are the options for Exclude the Following Participants. The options are: Creator, Previous Participant, and Expression.

Next to the Expression option is a blank field and the Expression Editor icon. 

The bottom section of the dialog box contains the List Assignees title and table. To the right of the List Assignees title are the Add and Delete buttons.

The table has three columns: Participant Type, Data Type, and Value. There is one row in the table.

The following items are bordered in red, to call attention to them:
By Expression in the Data Type column
The Expression Editor icon in the Value column