standard button with onclick
<![CDATA[<input type="button" value="search" onclick="alert('submitted');">]]>
image with onclick
<![CDATA[<img src="button.gif" alt="" onclick="alert('submitted');">]]>
image with onclick & alt
<![CDATA[<img src="button.gif" alt="search" onclick="alert('submitted');">]]>
image with onclick & alt & role
<![CDATA[<img src="button.gif" alt="search" role="button" onclick="alert('submitted');">]]>
image with onclick & alt & role & tabindex
<![CDATA[<img src="button.gif" alt="search" role="button" tabindex="0"
onclick="alert('submitted');">]]>
image with onclick & alt & role & tabindex & onkeypress
<![CDATA[<img src="button.gif" alt="search" role="button" tabindex="0"
onkeypress="if(event.keyCode==32||event.keyCode==13){alert('submitted')};"
onclick="alert('submitted');">]]>