<Path Stretch="Fill" Fill="{TemplateBinding Background}" Stroke="{TemplateBinding Stroke}" Data="M148.5,0.5 L148.50002,0.50000536 L151.5,0.50000536 L151.5,2.582355 L179.5,19.500002 L151.5,36.904938 L151.5,38.500004 L0.5,38.500004 L0.5,0.50000536 L148.5,0.50000536 z"/>
<
Path
Stretch
=
"Fill"
Fill
"{TemplateBinding Background}"
Stroke
"{TemplateBinding Stroke}"
Data
"M148.5,0.5 L148.50002,0.50000536 L151.5,0.50000536 L151.5,2.582355 L179.5,19.500002 L151.5,36.904938 L151.5,38.500004 L0.5,38.500004 L0.5,0.50000536 L148.5,0.50000536 z"
/>
The Path.Data property uses a special syntax to define how the path is drawn. For example, the first part, "M148.5,0.5" sets the start point of the drawing to the point (148.5, 0.5).
For more details, check out the MSDN topic on Path Markup Syntax:
http://msdn.microsoft.com/en-us/library/cc189041(v=vs.95).aspx