dds__icons will someday replace all of the other icon fonts.
Each dds__icon on this page is a text character (space " ") with two classes applied to it: "dds__icons" plus the specific "dds_IconName". This method is being used because when icons are added to the set, this is done alphabetically, causing downstream icons to change their character code.
The following filled icons are not part of the default icon set, but rather alternate states for existing icons:
Instead of displaying an icon as a text character, you can alternatively get it to display by applying the class "dds__icons" with the combo class "dds__IconName" to an element. For example, here are these two classes applied to a variety of elements: