All you need to do is fill in the blanks with something to trigger the add in the first place. Used to dynamically add external files to the current scene without the limitations of the Inline node. The URL system is very similar to that used to create VRML content from a string. THe major difference is that instead of returning a node and adding that to the scene you actually get the information back through an event. That event must be an MFNode eventIn.
Lets look at our problem again.
The first is an array of strings. This array is a list of URLs that can be retrieved. Like the rest of the nodes that use URL strings, this refers to the urls in decreasing order of preference. This must be a pre-existing, legal VRML node reference. This node could be anything, including a node previously created with a createVrmlFromString call, that has not been added to the scene yet.