1. OpenType fonts come in two flavors: with TrueType outlines (.ttf extension, they are backwards compatible to TrueType fonts) and with PostScript outlines (.otf extension). Apart from the sort of outlines used to construct glyphs, these flavors are interchangeable and have the same abilities.

2. Any OpenType font can (but does not have to) include OpenType Layout features. OpenType Layout features are a mechanism to style your text with different glyphs than the default ones provided by the font. For each character (e.g. a letter), alternate glyphs can be included in the font. Those alternate glyphs can represent one character (e.g. a small-cap A or a swash A) or more characters (e.g. an fi or st ligature).

3. For many non-European scripts (such as Arabic or Indic), OpenType Layout features are applied automatically during typesetting, without the user's intervention. In that case, the alternate glyphs are necessary for correct orthographic rendering of that script.

4. For European scripts, some applications allow the user to selectively enable and disable features. Rather than inserting the alternate glyphs directly, the user would typically choose an appropriate feature, i.e. a styling function. There is a registered set of OpenType Layout features and each has a particular purpose, for example one is for replacing uppercase letters with small-cap letters, another for replacing lining (uppercase) figures with oldstyle (lowercase) figures, another for common ligatures, another for rare ligatures, yet another for swashes, others for so-called stylistic sets (which can be arbitrary decorative or special-purpose variants) and so on. Enabling a feature replaces the default glyphs with some alternate glyphs (depending on which feature is enabled), or repositions the glyphs (e.g. shifts them up or increases spacing).

5. OpenType Layout is not a proprietary technology. It is part of the international standard ISO/IEC 14496-22.

6. Many applications enable user-controlled OpenType Layout features, for example on Windows Microsoft Word 2010, Microsoft Publisher 2010, Microsoft PowerPoint 2010, Adobe InDesign, Adobe Illustrator, Adobe Photoshop, CorelDRAW Graphics Suite X6, Serif Page Plus X6, QuarkXPress 9, Microsoft Expression Blend, Adobe Flash, and quite a few others. On Mac OS X, all applications that use the system Fonts palette can use OpenType Layout features.

7. It's not completely trivial for software developers to add support for user-controlled OpenType Layout features, mostly because the developers need to add a user interface for the features, and they need to make changes to their application's text storage system so that the application "knows" which features have been enabled on which text. But "under the hood", adding support for them is not complicated. Windows includes a system library called Uniscribe which provides a programming API that allows developers to apply user-controlled OpenType Layout features to the text.

8. With the release of Corel DRAW Graphics Suite X6, the two most popular drawing applications for Windows (Adobe Illustrator and Corel DRAW) have support for user-controlled OpenType Layout features. Xara is clearly lagging behind. I'd encourage the Xara developers to consider adding comprehensive OpenType Layout support in the next generation of their software.

9. I'm an OpenType and font development expert and am potentially available for consulting services in that area.

Regards,
Adam Twardoch
http://www.twardoch.com/