View invisible characters and object boundaries
You can display the boundaries of text, graphic, and media elements. You can also display “invisible” characters such as paragraph returns and spaces..
View boundaries or invisibles
Do one of the following:
View borders around the elements in a page: Choose Show Layout Boundaries from the View pop-up menu in the toolbar.
View invisibles: Choose Show Invisibles from the View pop-up menu in the toolbar.
Tip: To make invisibles stand out better, you can change their color. Choose iBooks Author > Preferences, click General, click the Invisibles color well, and select a color.
The table below shows what each invisible character represents.
Nonbreaking space (Option–Space bar)
Line break (Shift-Return)
Paragraph break (Return)
Anchored object marker