The earliest surviving literature by Vietnamese writers is written in Classical Chinese. Almost all of the official documents in Vietnamese history were written in Classical Chinese, as were the first poems. Not only is the Chinese script foreign to modern Vietnamese speakers, these works are mostly unintelligible even when directly transliterated from Chinese into the modern Vietnamese script due to their Chinese syntax and vocabulary. As a result, these works must be translated into colloquial Vietnamese in order to be understood by the general public. Works written in Nom script - a locally invented demotic script based on Chinese characters - was developed for writing the spoken Vietnamese language from the 13th Century onwards. For the most part, these chu nom texts can be directly transliterated into the modern Vietnamese script and be readily understood by modern Vietnamese speakers. However, since chu nom was never standardized, there are ambiguities as to which words are meant when a writer used certain characters. This resulted in many variations when transliterating works in chu nom into quoc ngu. Some highly regarded works in Vietnamese literature were written in chu nom, including Nguyen Du's Truyen Kieu, Đoan Thi Điem's chu nom translation of the poem Chinh Phu Ngam Khuc (征婦吟曲 - Lament of a Warrior Wife) from the Classical Chinese poem composed by her friend Đang Tran Con (famous in its own right), and poems by the renowned poet Ho Xuan Huong.