Editing Complex text layout (section)

==Implementations==
<!-- Lists in this section are in alphabetical order to avoid POV issues. -->
Most text-rendering software that is capable of CTL will include information about specific scripts, and so will be able to render them correctly without [[computer font|font files]] needing to supply instructions on how to lay out characters. Such software is usually provided in a [[library (computing)|library]]; examples include:
* [[Core Text]] for [[macOS]]
* [[Uniscribe]] (with Universal Shaping Engine) and [[DirectWrite]] for [[Microsoft Windows]]
* [[HarfBuzz]], a [[cross-platform]] library
* [[Pango]], a cross-platform library which nowadays incorporates [[HarfBuzz]]

However, such software is unable to properly render any script for which it lacks instructions, which can include many minority scripts. The alternative approach is to include the rendering instructions in the font file itself. Rendering software still needs to be capable of reading and following the instructions, but this is relatively simple.

Examples of this latter approach include [[Apple Advanced Typography]] (AAT) and [[Graphite (SIL)|Graphite]]. Both of these names encompass both the instruction format and the software supporting it; AAT is included on [[Apple Inc.|Apple]] [[operating system]]s, while Graphite is available for [[Microsoft Windows]] and [[Linux]]-based systems.

The [[OpenType]] format is primarily intended for systems using the first approach (layout knowledge in the renderer, not the font), but it has a few features that assist with CTL, such as contextual ligatures. AAT and Graphite instructions can be embedded in OpenType font files.