Fonts & Encodings

3.4. Rendering properties

3.4.1. The Arabic and Syriac scripts

The characters of these scripts have two additional properties: joining type and joining group. To understand what these terms mean, let us recall the properties of these two scripts.

The scripts include three types of letters:

• those that have four contextual forms: initial, medial, final, and isolated, the isolated form being both initial and final;

• those that have two contextual forms: final and isolated;

• those that have only one contextual form.

Let B be a letter with four forms and R a letter with two forms. Let us use 0, 1, 2, and 3 to represent the isolated, initial, medial, and final forms, respectively. Thus we have at our disposal the forms B₀, B₁, B₂, B₃, and also R₀ and R₃.

Contrary to what one might expect, contextual forms do not refer to words but to contiguous strings of letters. An initial letter may very well appear in the middle of a word; that will occur if the preceding letter is a final form. Thus we shall concern ourselves here with strings of letters.

Here are the three rules to follow in order to build up strings:

1. start the string with an initial letter;

2. within the string, continue with a medial letter, or, if the required letter has no medial form, use its final form, which will end the string;

3. the last letter of the string must necessarily be a final form.

Let us take a few typical examples of words of three letters: BBB, BBR, BRB, RBB, BRR, RBR, RRB, RRR.

In the first of these words, the first ...