帮助系统

这些类为应用程序提供在线帮助，采用 3 细节级别：

1. Tool Tips and Status Bar message - flyweight help, extremely brief, entirely integrated in the user interface, requiring little or no user interaction to invoke.
2. What's This? - 轻量，但可以是三段式解释。
3. Online Help - can encompass any amount of information, but is typically slower to call up, somewhat separated from the user's work, and often users feel that using online help is a digression from their real task.