您将创建一个简单的表单，只有一个字段Enter a number和一个Validate文本按钮。

You will create a simple form with a single field Enter a number and a button with the text Validate.

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只有当控件失去输入焦点时，验证步骤才能发生。也就是说，当用户已经处理一个字段而移到下一个字段时。

The validation then takes place only when the control loses focus, that is, when a user is done with the field and moves on to the next one.

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