apostrophe used to divide syllables within a word to avoid ambiguity in various alphabetic systems used in China; in pinyin, to be used between two syllables in a word (unless a hyphen is being used) whenever the second syllable begins with an a, o or e (regardless of whether any ambiguity exists) and not in any other circumstance
Examples
a，o，e開頭的音節連接在其它音節後面的時候，如果音節的界限發生混淆，用隔音符號（’）隔開，例如：pi’ao（皮襖）。
[In Hanyu Pinyin], when a syllable beginning in a, o or e is preceded by another syllable, if the division between the syllables is unclear, use the syllable-dividing apostrophe (’) to divide [the syllables]. For example: pi’ao 皮襖／皮袄 (pí'ǎo).
壯文的多音詞主要是根據聲韻結構和聲調符號來識別音節……當據此仍不好區分音節時，就得利用隔音符號“’”來劃分
In Zhuang, syllables in multisyllabic words are distinguished according to the syllable structure and tone symbols... When the syllables still cannot be distinguished accordingly, an apostrophe "'" needs to be used to divide the syllables