title: How do I make an item in a toolbar fill all available space in WPF
body: <p>I'm trying to make an item on ToolBar (specifically a Label, TextBlock, or a TextBox) That will fill all available horizontal space.  I've gotten the ToolBar itself to stretch out by taking it out of its ToolBarTray, but I can't figure out how to make items stretch.</p>
  
  <p>I tried setting Width to Percenatage or Star values, but it doesn't accept that.  Setting Horizontal(Content)Alignment to Stretch in various places seems to have no effect either.</p>