3.5.4.1. A Shield Bash is defined as using a Shield to strike an opponent from a distance further than two steps away.
3.5.4.2. A Shield Check is defined as using a Shield to strike an opponent starting from a distance less than two steps away.
It doesn't say what part of the shield you are/aren't aloud to hit with.
So this means, if I am assuming correctly. You can throw a punch, with the shield being an extension of your arm, in to someones ribs?
I was watching this being done on youtube.
I can't remember where I found the video but it was some sort of Sword and Board class/demo.
It looks to me as if this would be ok.
According to the rules.
Answer: Yes you can use it as an extension of your arm. What your talking about is commonly called shield edging. Using the edge of your shield to "Punch" someone. - SnoJoo
For anyone who didn't know.