Editing Unicode (section)

=== Ligatures ===
<div class='skin-invert-image'>{{Multiple image
|total_width = 300
|image1      = JanaSanskritSans ddhrya.svg
|caption1    = The [[Devanagari|Devanāgarī]] ''{{IAST|ddhrya}}''-ligature (द् + ध् + र् + य = द्ध्र्य) of JanaSanskritSans<ref>{{Cite web |title=JanaSanskritSans |url=http://tdil.mit.gov.in/download/janasanskrit.htm |url-status=dead |archive-url=https://web.archive.org/web/20110716160603/http://tdil.mit.gov.in/download/janasanskrit.htm |archive-date=16 July 2011}}</ref>
|image2      = 23a-Lam-Alif.svg
|caption2    = The [[Arabic script in Unicode|Arabic]] {{lang|ar-Latn|[[lām]]-[[aleph#Arabic|alif]]}} ligature ({{lang|ar|ل}} &lrm;+&lrm; {{lang|ar|ا}} &lrm;=&lrm; {{lang|ar|لا}})
}}</div>
Many scripts, including [[Arabic script in Unicode|Arabic]] and [[Devanagari|Devanāgarī]], have special orthographic rules that require certain combinations of letterforms to be combined into special [[ligature (typography)|ligature forms]]. The rules governing ligature formation can be quite complex, requiring special script-shaping technologies such as ACE (Arabic Calligraphic Engine by DecoType in the 1980s and used to generate all the Arabic examples in the printed editions of ''The Unicode Standard''), which became the [[proof of concept]] for [[OpenType]] (by Adobe and Microsoft), [[Graphite (SIL)|Graphite]] (by [[SIL International]]), or [[Apple Advanced Typography|AAT]] (by Apple).

Instructions are also embedded in fonts to tell the operating system how to properly output different character sequences. A simple solution to the placement of combining marks or diacritics is assigning the marks a width of zero and placing the glyph itself to the left or right of the left sidebearing (depending on the direction of the script they are intended to be used with). A mark handled this way will appear over whatever character precedes it, but will not adjust its position relative to the width or height of the base glyph; it may be visually awkward and it may overlap some glyphs. Real stacking is impossible but can be approximated in limited cases (for example, Thai top-combining vowels and tone marks can just be at different heights to start with). Generally, this approach is only effective in monospaced fonts but may be used as a fallback rendering method when more complex methods fail.