A DefineFontInfo tag will be used to complete the definition of a DefineFont tag. It uses the exact same identifier (f_font_info_id_ref = f_font_id). You must have the corresponding font definition appearing before the DefineFontInfo since it will use the number of glyphs defined in the DefineFont to know the size of the map definition in the DefineFontInfo tag.
When it looks like it perfectly matches an existing system font, the plugin may use that system font (as long as no rotation is used, it will work fine.) It is also possible to force the use of the system font by declaring an empty DefineFont tag (i.e. no glyph declaration at all.)
The use of system fonts usually ensures a much better quality of smaller prints. However, since version 8, there are many features in the Flash player taking care of really small fonts.
Note, however, that a system font (also called a device font) cannot be rotated. Also, the scaling and translation of a system font does not always respect the exact position. It is likely that the font will be moved to the next pixel left or right to avoid blurriness. That means it will look quite jaggedly when slowly moving such text.
The f_font_info_wide flag must be set to 1 in version 6 and over.
Note that the flag f_font_info_small_text of version 7+ is the same bit as the flag f_font_info_unicode in SWF version 5 or less.
Since version 6, the font name has to be encoded in UTF-8 instead of whatever encoding you want. It is also suggested that you use the DefineFontInfo2 tag instead.