通过模式，验证解析器可以检查元素 InvoiceNo 是否是正整数，元素 ProductID 的首字符是否为 A 到 Z 之间的字母，后面为六个阿拉伯数字。

Through the schema, a validating parser can verify that the element InvoiceNo is a positive integer and the element ProductID consists of one letter between A and Z followed by six digits.

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