Updating Customer in Zoho Invoice

Updating Customer in Zoho Invoice

I am trying to understand how to update a customers information in Zoho Invoice from Zoho Creator.  I am successful at using the geturl and posturl for most API functions.  However when I need to update a customer the required I am required to pass and XMLString as one of the paramaters.  I am unclear what this would even look like.  If someone could give me an example.  I am familar and successful with XPath Builder and have several scripts running that integrate with Zoho Invoice, but this is the first Method that has required and XMLString to be passed.  The link below is where I found the requirement, but there is no example.

http://www.zoho.com/invoice/api/customers/customers.html#how-do-i-update-a-customer-and-get-a-formatted-response?