Multi-line and single-line fields
The right-hand pane (or 'detail paine') can contain two types of fields:
Single-line fields: these can contain one line of text. Most fields in a Custom Addressbook file are single-line fields (unless you define this otherwise. More information on how to define your own fields can be found here: Customizing Custom Addressbook).
Multi-line fields: these can contain two or more lines of text. If a multi-line field contains a lot of text, then it often can be edited more easily using a separate editor called The "Edit field" window
In the screenshot below, all fields (or attributes) are single-line fields, except for Address and Comments.