1. A computer-implemented method for transforming an XML file into an add-in function for use in a spreadsheet application comprising: scanning an add-in XML file for an instruction; determining an interface XML file to be exposed by the instruction; accepting the interface XML file from a COM server; determining if the instruction comprises a function qualifier; wherein the function qualifier modifies a function specification in the interface XML file; applying the function qualifier to the function specification; converting the function specification to an intermediate function; applying an implementation specifier to the intermediate function, wherein the implementation specifier overrides the default implementation of the interface XML file; converting the intermediate function to an add-in function; and transmitting the add-in function to the spreadsheet application for processing.