Specify which Property goes between the opening and closing tag in Xaml

Consider the following Xaml

<Grid>
    <TextBox>Text</TextBox>
    <Button>Content</Button>
</Grid>

It will set the

• Text Property of a TextBox (only WPF)
• Content Property of a Button
• Children Property of a Grid

But how is this specified? How do you specify which Property that goes between the opening and closing tag in Xaml?
Is this set by some metadata in the Dependency Property or what?

Thanks