和原来的SGML一样，XML也是一种元语言，是定义其他语言的语法基础。
Like SGML before it, XML is a meta-language: it is a syntactic basis for defining further languages.
正式句法模式描述语法，例如生成语法，是一种元语言。
Formal syntactic models for the description of grammar, eg generative grammar, are a type of metalanguage.
语法与元语言知识的教学以及母语的正迁移作用是交际法教学中经常被忽略的问题。
Grammar and metalinguistic knowledge as well as mother tongue's positive transfer are often neglected in communicative language teaching.
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