A regular expression is a pattern description using a meta language. 常规表达式是一种使用元语言的模式描述。
On the contrary, the essential task of metalanguage is to explore the originality of expression and explanation, and the natural language is the original metalanguage. 元语言的根本问题是表达和解释的初始性，自然语言是最初始的元语言。
