Conditional layouts contain conditions that you can attach to any non-group field within the layout. A condition is a true or false statement queried against the value of the field. If all conditions in the layout are true for a particular record, the record is displayed using that layout. If not all of the conditions are true, the record uses the default layout (or another conditional layout).
If you are using a structure file that does not contain a default layout, any records that cannot use a conditional layout from the structure file are displayed unformatted.
For records that could use more than one layout (that is, they match all conditions in more than one layout), the record uses the first layout possible, based on the order that the conditional layouts are displayed in the Selected Layouts pane.