The Abyssinica SIL font is designed to work on systems and with applications that provide support for TrueType fonts and for Unicode character encoding. This includes Microsoft Windows® 9x or greater, as well as recent versions of the Mac OS (version 9.0 and later), and also some implementations of Unix / Linux (TrueType font support on Unix and Linux may depend upon the particular applications in use). Abyssinica SIL is a TrueType font with smart font capabilities added using OpenType and Graphite font technologies. This means that complex typographic issues such as the placement of combining marks or the choice of alternate glyphs are handled by the font, provided you are running an application that provides an adequate level of support for one of these smart font technologies.
Standard use of the Ethiopic script does not require any of these smart font technologies. However, to take advantage of the advanced typographic capabilities of this font, you must be using applications that provide an adequate level of support for Graphite or OpenType. Microsoft Office 2010 supports dynamic positioning of most diacritics (but not U+135D or U+135E) over the Ethiopic range (U+1200..U+135A) but not over Ethiopic Supplement or Ethiopic Extended characters. However, Microsoft Publisher 2003 does support dynamic positioning of U+135F. There are currently few applications which make use of the Graphite capabilities of the font.
See Smart Font Features for further information.
See Using Font Features. Although that page is not targeted at Ethiopic support, it does provide a comprehensive list of applications that make full use of the OpenType and Graphite font technologies.