In addition, there are a number of dialect characters (方言字) that are not used in formal written Chinese but represent colloquial terms in non-Mandarin varieties of Chinese. One such variety is Written Cantonese, in widespread use in Hong Kong even for certain formal documents, due to the former British colonial administration's recognition of Cantonese for use for official purposes. In Taiwan, there is also an informal body of characters used to represent Hokkien Chinese. Many varieties have specific characters for words exclusive to them. For example, the vernacular character 㓾, pronounced cii11 in Hakka, means "to kill". Furthermore, Shanghainese and Sichuanese also have their own series of written text, but these are not widely used in actual texts, Mandarin being the preference for all mainland regions.
What was the preference for all mainland regions?
Mandarin