Tree walking

Pressing the above button will:

• launch the do_document function
• The do_document function will extract the body element and then call the mark_tags function with argument == body element
• The mark_tags function will examine all children of body and if there are are, also the children of these children, etc.
• Each time we find an element node, we will append its name to the node_list variable
• Finally, we display node_list in an alert popup window