categories 
This property is part of IconSet class in Iconify Tools.
Property categories contains list of categories.
Structure 
Property categories is a Set of IconCategory entries.
IconCategory type 
Type IconCategory has the following properties:
- title, string. Category title.
 - count, number. Number of icons.
 
Number of icons is approximate, to get exact number use listCategory() function. Running listCategory() updates IconCategory entry and deletes empty categories.