Typographical Features of the Cocoa Text System
http://developer.apple.com/documentation/Cocoa/Conceptual/TextArchitecture/Concepts/TextSystemFeatures.html

Apple Inc.
2006

Abstract:

It is common, especially in technical writing, to mix languages with differing text direction, such as English and Hebrew, in the same line. Some writing systems even alternate layout direction in every other line (an arrangement called boustrophedonic writing). Some languages do not group glyphs into words separated by spaces. Moreover, some applications call for arbitrary arrangements of glyphs; a graphic layout may require glyphs to be arranged on a nonlinear path.