TrueType Versus TrueType Open

A TrueType font is a collection of several tables that contain different types of data: glyph outlines, metrics, bitmaps, mapping information, and much more. TrueType Open fonts contain all this basic information, plus additional tables containing information for advanced typography.

Text-processing applications—referred to as clients of TrueType Open—can retrieve and parse the information in TrueType Open tables. So, for example, a text-processing client can choose the correct character shapes and space them properly.

As much as possible, the tables of TrueType Open define only the information that is specific to the font layout. The tables do not try to encode information that remains constant within the conventions of a particular language or the typography of a particular script. Such information that would be replicated across all fonts in a given language belongs in the text-processing application for that language, not in the fonts.