The "Edit field" window
Fields (inside the right-hand pane or 'detail pane') that span more than one line are called 'multi-line fields'. When you double click on a multi-line field, Custom Addressbook will open a large notepad-like editor named Edit field. This will enable you to view or edit the multiline attribute in more detail.
You can achieve the same result by pressing F2 (but only inside a multiline editbox).
When the Edit field window is open you can click OK or Cancel to close it.
You can also press F2 to close the Edit field window (but only when the editor inside this dialog has focus).