Lisa See describes the use of Nüshu among 19th-century women in "Snow Flower and the Secret Fan". The Nüshu script is used to write a distinct local Chinese variety known as Xiangnan Tuhua () that is spoken by the people of the Xiao River and Yongming River region of northern Jiangyong County, Hunan. This dialect, which differs enough from those of other parts of Hunan that there is little mutual intelligibility, is known to its speakers as "Dong language". It is written only in the Nüshu script. There are differing opinions on the classification of Xiangnan Tuhua, as it has features of several different Chinese varieties. Some scholars classify it under Xiang Chinese or Pinghua and other scholars consider it a hybrid dialect. In addition to speaking Tuhua, most local people in Jiangyong are bilingual in the Hunan dialect of Southwestern Mandarin, which they use for communication with people from outside the area where Tuhua is spoken, as well as for some formal occasions. If Hunan Southwestern Mandarin is written, then it is always written using standard Chinese characters and not with the Nüshu script. Jiangyong County has a mixed population of Han Chinese and Yao people, but Nüshu is used only to write the local Chinese dialect (Xiangnan Tuhua, ), and there are no known examples of the script being used to write the local Yao language. A large number of the Nüshu works were "third day missives" (). They were cloth bound booklets created by laotong, "sworn sisters" () and mothers and given to their counterpart "sworn sisters" or daughters upon their marriage. They wrote down songs in Nüshu, which were delivered on the third day after the young woman's marriage. This way, they expressed their hopes for the happiness of the young woman who had left the village to be married and their sorrow for being parted from her. Other works, including poems and lyrics, were handwoven into belts and straps, or embroidered onto everyday items and clothing. Nüshu is included in the Unicode Standard under the name "Nushu" (because Unicode character names, block names, and script names can only use ASCII letters). 396 Nüshu letters were added to the Nushu block as part of Unicode version 10.0 which was released in June 2017. An iteration mark for Nüshu, , is in the Ideographic Symbols and Punctuation block.