The purpose of this guide is to provide the necessary information to allow the creation of applications that work in Arabic or Hebrew. Reading and writing of Arabic or Hebrew text is done from Right-To-Left. This means that the "start" point of a Hebrew/Arabic text is on the right side of the page/screen while the natural end of the text is on the left side.
In many cases, Arabic and Hebrew scripts contain embedded pieces of text which are written and read from Left-To-Right. In fact, having mixed Right-To-Left (RtL) and Left-To-Right (LtR) "segments" of text is very common in these languages. Examples of such cases is the use of numbers (which are usually LtR, as in English) and the use of embedded Latin text within Arabic/Hebrew text, which is also very common.
Having such text, with embedded Right-To-Left and Left-To-Right pieces (segments), is the reason for referring to the Arabic and Hebrew languages as "Bidirectional Languages" (or bidi languages, for short).
In this document, we will use the term 'National Language' or 'Bidi Language' to refer to 'Arabic or Hebrew'. (to distinguish it from English). Also, 'Arabic/Hebrew' is used to signify 'either Arabic or Hebrew'.