Editing Complex text layout (section)

==Characteristics requiring CTL==
The main characteristics of CTL complexity are:
* [[Bi-directional text]], where characters may be written from either right-to-left or left-to-right direction.
* [[Context-sensitive shaping]] and [[ligature (typography)|ligature]]s, where a character may change its shape, dependent on its location and/or the surrounding characters. For example, a character in [[Arabic script]] can have as many as four different shape-forms, depending on context.
* Ordering, where the displayed order of the characters is not the same as the logical order. For example, in Devanagari, which is written from left to right, the grapheme for "short i" appears to the left of ("before") the consonant that it follows: in {{lang|sa|कि}} ''ki'', the {{lang|sa|ि}} ''-i'' should render on the left, its bow reaching until above the {{lang|sa|क}} ''k-'' to the right.

Not all occurrences of these characteristics require CTL. For example, the [[Greek alphabet]] has context-sensitive shaping of the letter [[sigma]], which appears as ς at the end of a word and σ elsewhere. However, these two forms are normally stored as different characters; for instance, [[Unicode]] has both {{unichar|03C2|GREEK SMALL LETTER FINAL SIGMA}} and {{unichar|03C3|GREEK SMALL LETTER SIGMA}}, and does not treat them as [[Unicode equivalence|equivalent]]. For collation and comparison purposes, software should consider the string "δῖος Ἀχιλλεύς" equivalent to "δῖοσ Ἀχιλλεύσ",<ref>{{cite web|url = https://www.unicode.org/faq/greek.html#5|title = FAQ - Greek Language & Script|accessdate = 2013-09-13|publisher = Unicode Consortium|date = 2012-12-03|quote = It is easier to simply equate the two sigma codes for operations which are concerned with word content, for example.}}</ref> but for typesetting purposes they are distinct and CTL is not required to choose the correct form.