Complex text layout

For assistance with enabling complex text layout on your computer, see Help:Multilingual support.
The Devanagari ddhrya-ligature, as displayed in the JanaSanskritSans font, which should be invoked by the layout engine to render the sequence द + ् + ध + ् + र + ् + य = द्ध्र्य.
The word العربية al-arabiyyah, "the Arabic [language]" in Arabic, in successive stages of rendering. The first line shows the letters in left-to-right order and unjoined, as they might appear in an application without complex text layout. In the second line, bidirectional display has been applied, and in the third the glyph-shaping mechanism has rendered the letters according to context.

Complex text layout (CTL) or complex text rendering is the typesetting of writing systems in which the shape or positioning of a grapheme depends on its relation to other graphemes. The term is used in the field of software internationalization, where each grapheme is a character.

Scripts which require CTL for proper display may be known as complex scripts. Examples include the Arabic alphabet and scripts of the Brahmic family, such as Devanagari, Khmer script or the Thai alphabet. Many scripts do not require CTL. For instance, the Latin alphabet or Chinese characters can be typeset by simply displaying each character one after another in straight rows or columns. However, even these scripts have alternate forms or optional features (such as cursive writing) which require CTL to produce on computers.