What is a rich text field?

A text field where, in contrast to a normal text field, most of the formatting can be done by the author.

When setting up a Lytho template, the templates administrator can determine if a text input field will be a normal text field or a rich text field. A rich text field distinguishes itself by the ability, for the author/user creating a template, to format the text with character and paragraph styles. 

It is necessary that these styles are present in the source file (.idml) of the template. A designer can add character and/or paragraph styles to the source file (before uploading it to Lytho) to provide the Lytho user with some extra formatting options in the user interface. The users are given free rein to format the text of the publications within the guidelines of the predefined styles.

These character and paragraph styles contain all sorts of formatting attributes like font, size, color, and spacing.

To learn everything about Adobe InDesign's character and paragraph styles:

Check out their user guide