Display Priority
Basically, the order in which elements are inserted also determines the order in which they are displayed. For instance, a filled in rectangle which is drawn over text that was inserted previously, will cover the text, which is then no longer visible. This default setting can be changed subsequently with the 
buttons for display priority, which are always shown in the toolbar when an element is selected. This enables you to specify the order in which elements are displayed, to suit a particular case, e.g. inserting text over a filled in rectangle when creating a title block.