Currently, the filter on styles displayed in the Style pane is a drop-down list, with elements:

Hierarchical
All
Hidden
Applied
Text
Chapter
List
Index
Special
HTML
Conditional

(with all but the first having a " Styles" prefix; and only the first four appearing for non-Paragraph styles)

and a top row of buttons:

Paragraph
Character
Frame
Page
List
Table

The top row is (mostly) orthogonal to the choices in the bottom menu. That's good. However, the bottom menu does not really list the values in a single category.

Instead, we should have widgets for the different features of style:

* Hierarchical: A binary checkbox ("Hierarchical view" Yes/No).
* Hidden: Either a binary checkbox ("Show hidden" Yes/No), or some three-state widget (hidden, not hidden, all).
* Used:  Either a binary checkbox ("In-use only" Yes/No), or a three-state widget (Only used, only unused, all).
* Paragraph style sub-category: This could be a drop-down list, but only have it for paragraph styles. Perhaps make the top button, for paragraph styles, into a menu-button with this function?  ... TBH, this subcategorization seems a bit messy to me, but whatever.

This will address bugs 46719 and 80950. And - it will allow me to keep a hierarchical view not of all styles, but sets of styles I'm interested in.