Set text wrapping
You can control whether text that is contained in a TextBox or TextBlock object in Microsoft Expression Blend will wrap onto multiple lines when the text cannot fit within the width of the text box object.
Select the TextBox or TextBlock object that you want to format, by using either the Selection tool or the Direct Selection tool .
In the Properties panel, under Text, click Show advanced properties to see the TextWrapping property.
If you do not see the TextWrapping property, you might be in text-editing mode (F2), which lets you change the text that is displayed in the control. To exit text-editing mode, press ESC.
Click the TextWrapping value, and then click one of the following options:
No Wrap, to prevent text from wrapping. This option confines each line of text to a single line regardless of the width of the text box.
WrapWithOverflow (Windows Presentation Foundation only), to allow the text to break onto multiple lines when the lines of text in the object are longer than the width of the text box. This makes sure that the text will fit within the width of the text box. Note that this option does not wrap single words on individual lines; if a word on a line by itself is longer than the width of the text box, part of the word will not be displayed.
Wrap, to make a line of text break across multiple lines when the line is longer than the width of the text box. This option also wraps an individual word onto multiple lines if the word is longer than the width of the text box.