The character code, which is a Unicode UTF-32 code point.

This is the ID of the font (i.e. set of characters) of which character is a member. One potential use for this value would be to have each font use a distinct value for the characters in that font, so that an application could refer to a set of character keys from all the fonts and still be able to distinguish which character came from which font.

The instance number, which can be used to uniquely identify a particular instance of a character with a given character code within a particular font.

The variant number, which can be used to indicate a distinct appearance of a character code. For example, a particular font might contain two visually distinct appearances for the digit zero "0", one of which might simply be an ellipse and another that is an ellipse with a diagonal stroke through it.