一般情况下，DOM实现必须检验操作的正确性，并在应用程序传递错误参数或者执行非法操作时抛出异常。
Normally, a DOM implementation must verify the correctness of operations and throw an exception if an application passes the wrong parameters or performs an illegal operation.
验证jsp语法的正确性，并且报告所有的验证错误。
Validate that the JSP syntax is correct and report any validation errors.
主要原因是软件模式经常会导致不可预知的严重性错误：我们都清楚，任何一个模式的实际价值与它的正确性直接成比例。
The main reason is that software models can often be terribly inaccurate in unpredictable ways: clearly, the practical value of any model is directly proportional to its accuracy.
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