For Mac OS users, there is a system setting that may not allow you to tab onto several types of elements in a web page. To change this setting:
Each Elem. class will wear the designated color: PreK-Orange; Kindergarten-Green; 1st Gr.-Blue; 2nd Gr.-Red; 3rd Gr.-Black; 4th Gr.-White; 5th Gr.-Grey; 6th Gr.-Purple.