Although authors cannot count on a specific font being used in a document, they can very easily specify generic font families to be used. This particular behavior is generally very well supported, since any user agent that didn’t let authors (or even readers) assign fonts would quickly find itself out of favor.
As for the other areas of font manipulation, support varies. Changing the size of fonts usually works well, but twentieth-century implementations ranged from frustratingly simplistic to very nearly correct in this area. The frustrating part for authors, though, is usually not how font sizing is supported, but how a unit they want to use (points) can yield very different results in different media, or even different operating systems and user agents. The dangers of using points are many, and using length units for web design is generally not a good idea. Percentages, em units, and ex units are usually best for changing font sizes, since these scale very well in all common display environments.
Now that we’ve worked our way through altering text and fonts, let’s turn to ways to style the elements that contain the text.