Below is an example of how to combine two different simple DOMs with 1 Repeat Action and 1 Map action.   

Explanation: The key to the simplicity of this solution is the use of the XPath union ( vertical bar | ) operator.  The union operator creates a single node list for the Repeat Loop to process from two or more XPath location specifications.   The unioned XPath specifications for the Source of the Repeat for Element action in this case are shown below.  The not so obvious part of the solution is the use of the createXPath() method.  This ECMAScript extension method is how xCommerce creates DOM nodes using the XPath syntax (Note: XPath was created to be an XML document hierarchy search language making it well suited to the Source side of an xCommerce Map action.  xCommerce's architects decided to also use XPath for writing XML document's on the Target side of a Map action - hence the need to create the createXPath() method.)  createXPath() takes a string (representing a valid XPath expression) as its argument.  In this case, we generate the string by simply returning the name of the node being processed (notice the use of the alias TWODOMs) by the Repeat Loop using the DOM Node property called nodeName.  createXPath() however, is limited in its XPath support.  It only allows the abbreviated ( slash separated strings ) XPath syntax and only accepts ordinal selection criteria.

Below is an example of how to combine two DOMs of the same  hierarchy with 1 Repeat Action and 1 Map action. 

Note:  In the sample applications that install with xCommerce there is a combine documents example.  The syntax in this example is incorrect.  The appropriate way to combine documents is shown in this article.