There are several styles of a Span object that can be set on text in a form field that has richText = true which can't be set through JavaScript.

During the Keystroke event, event.richChange includes attributes on each Span object for these missing styles. Unfortunately, manipulating these attributes does nothing and any manually set styles that are unsupported through JavaScript disappear when the richChange or richValue attributes are set through JavaScript

This includes, but is not limited to (with the attribute in the richChange Keystroke event object listed in brackets):
* left indent (marginl attribute)
* right indent (marginr attribute)
* first line indent (special attribute)
* spacing above (spacebefore attribute)
* spacing below (spaceafter attribute)

The attached screenshot shows the "Form Field Text Properties" dialog where the above elements can be set manually. It is a real shame that any manual changes are lost when the field is manipulated through JavaScript.