<Expander Header="More options" Margin="281,218,39,12">
    <Button Height="29" Width="111"> hello </Button>
</Expander>
上面的代码有效。但:
<Expander Header="More options" Margin="281,218,39,12">
    <RichTextBox Name="richTextBox1" Margin="100,50,200,30" Height="30" Width="80">
        <FlowDocument>
            <Paragraph>Hi how are you?</Paragraph>
        </FlowDocument>
    </RichTextBox>
</Expander>
这行不通。为什么?如何使这项工作?