Wikipedia
Xiao'erjing or Xiao'erjin or Xiaor jin or in its shortened form, Xiaojing, literally meaning "children's script" or "minor script" (cf. "original script" referring to the original Perso-Arabic script, , Xiao'erjing: بٌکٍْ; ), is the practice of writing Sinitic languages such as Mandarin (especially the Lanyin, Zhongyuan and Northeastern dialects) or the Dungan language in the Perso-Arabic Script. It is used on occasion by many ethnic minorities who adhere to the Islamic faith in China (mostly the Hui, but also the Dongxiang, and the Salar), and formerly by their Dungan descendants in Central Asia. Soviet writing reforms forced the Dungan to replace Xiao'erjing with a Roman alphabet and later a Cyrillic alphabet, which they continue to use up until today.
Xiao'erjing is written from right to left, as with other writing systems using the Perso-Arabic script. The Xiao'erjing writing system is unique among Arabic script-based writing systems in that all vowels, long and short, are explicitly marked at all times with diacritics, unlike some other Arabic-based writing like the Uyghur Ereb Yéziqi which uses full letters and not diacritics to mark short vowels. This makes it a true abjad. Both of these practices are in contrast to the practice of omitting the short vowels in the majority of the languages for which the Arabic script has been adopted (like Arabic, Persian, and Urdu). This is possibly due to the overarching importance of the vowel in a Chinese syllable.