一条语法规则，不管如何正确，除非能懂，否则毫无用处。
A grammar rule, however true (it is), is useless unless it can be understood.
除非把书本知识应用到实践中去，否则它仍然停留在理论层面，这样最终就毫无用处。
Unless it is applied to real experiences, book knowledge remains theoretical and, in the end, is useless.
虽然可以为一般dtd中的任何标记创建新的等价元素，但是除非内容模型包含也进行专门化的标记，否则这对作者来说毫无用处。
Although you could create a new element equivalent for any tag in a general DTD, this work is useless to you as an author unless the content models that would include the tag are also specialized.
应用推荐