<Grid> <TextBlock> Hello World. <LineBreak />This is the second line. The breaking of the lines in the XAML are <Run Foreground="Red">not significant</Run>. </TextBlock> </Grid>
A LineBreak indicates where line breaks are going to occur without regard to the TextWrapping property. A Run is used to wrap some piece of text that needs to be formatted differently than other parts of the TextBlock. The Run supports the basic properties that a TextBlock allows but only applies them to the text inside the Run element as shown above.