Is it possible to add a "default" text value to a
This is certainly possible. You can either:
1) Set the initial text normally, then on an event such as
OnTextSelected() you can delete that text, then it will be blank before they start typing. You can also go one step further and add something to
OnTextChanged() to see whether the text is blank and every time there is no content, your initial content can be set again.
2) Alternatively, you can create a custom style for your text block, with a text block inside of it, a property to set the text block text and an event hooked up to clear the text block text. This is nicer, but more work. I would recommend this if you wish to re-use this control.