How to get Source Node Element ID when listening to http-on-modify-request

Hi,
In my extension, I am listening to the topic http-on-modify-request. I'd 
like to be able to get a reference to the DOM Node element ID that was 
actually triggering the topic.

for example, if I have <a href="www.example.com" id="alink1">click here</a>
I want to be able to identify that "alink1" (TAG id of link, if present any) was the source when I get 
the message in my observe method.

Does anyone know how this can be done?

regards,
Kailas