An Arabic character may take one, two, or sometimes four different shapes, yet it is represented by one code. The shape of the character is determined depending on its position in the word. Another is the direction of writing.
Arabic text is written from right to left.
This conflicts with English, which is written in the opposite direction. When mixing text languages, characters are added in one language and pushed in the other. Some users speak only Arabic. They will not accept a cursor positioned at the leftmost position of the screen. They want to have an option allowing them to start at the rightmost position of the line, i.e. in brief, a mirror image of the screen.