Microsoft and Adobe jointly developed the OpenType font format, which was first released in April 1997. It is essentially an extension of the TrueType format-a digital font technology (designed by Apple Computer and now used by both Apple and Microsoft in their operating systems) that offers superior display quality on computer screens and printers. Expanding upon the capabilities of TrueType, OpenType provides better support for international character sets, protection for font data, and advanced typographic control. OpenType fonts can contain either TrueType outlines or PostScript outlines.
One of the advantages of fonts created with the OpenType format is that, by using Unicode, they can handle a large and varied glyph set. Because of the powerful architecture that the OpenType Layout model provides, these fonts also allow a rich mapping between characters and glyphs, thus enabling support for ligatures, positional forms, alternates, and other substitutions.
Another benefit of OpenType fonts is their ability to contain layout tables that give font designers greater typographic control. (For more information, see "International Features" later in this chapter.) Digital signatures can be included in OpenType fonts, which allow operating systems and applications to establish the integrity of the font, identify its source, and find out if it contains any embedding restrictions. Restrictions that the font designer embeds in a font that is digitally signed cannot be altered, which helps ensure the protection of your font data.
Yet another advantage resides in the fact that OpenType fonts are portable across platforms. They can also be embedded in documents or used for international content on Web sites. In addition, the OpenType font format supports all encoding schemes in common use today and, therefore, is not dependent on any single encoding scheme. However, all fonts that Microsoft currently ships are Unicode-encoded.