In WPF, you can use any control almost anywhere. So you can try the following:
<CheckBox> <StackPanel> <TextBlock>foo</TextBlock> <TextBlock>bar</TextBlock> </StackPanel> </CheckBox>
In addition, you need to remove the Height property from your checkbox. Of course, only one line is displayed if the height does not allow more to be displayed.
In WPF, in most cases, you do not (and should not) specify absolute sizes for your controls. They can be automatically configured.
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