The "Styled Text" theme contains the language commands used for managing and modifying multi-style text areas, also known as rich text areas.
You declare a rich text area by enabling its "Multi-style" option in the Property List (see Multi-style (Rich text area) in the Design Reference manual). You can use the OBJECT Is styled text command of the "Objects (Forms)" theme to find out whether or not a text area is in multi-style mode.