Browsers don't seem to currently support external or parameter entities in the internal subset, probably as a security measure.
浏览器目前似乎不支持内部子集中的外部实体或参数实体，这也许是一个安全措施。
It doesn't read DTDs in external files, but it also doesn't use any declarations within the document (called the internal subset) for validation.
它不读取外部文件中的DTD，也不使用文档中的任何声明(称为内部子集)来进行检验。
Another hoped-for core improvement that didn't make it is the ability for the user to request that the browser loads the external DTD subset.
未能实现的另一个期望的核心改进是允许用户请求浏览器装入外部dtd子集。
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