Determine FORM That Contains A Specific INPUT Element?

I created this test routine to return the form containing a certain
input element:

function GetElementForm(element)
{
// Return the form that contains element.

varmyElement = element;

while (myElement)
{
myElement = myElement.parentNode;
if (myElement)
{
var sTagName = myElement.tagName;
if (sTagName)
{
if (sTagName.toLowerCase() == "form")
{
break;
}}}}
return myElement;}

This seems to work for "well formed" HTML, but fails for example, when
a form is defined within a table.