The core process of XpressDox is the merging of data into a template to produce a final merged document. The XpressDox merging engine thus needs two things: a set of data to merge, and a template into which to merge the data. The data which XpressDox merges into a template is referred to as a Data Set, and must be in XML format. The template then addresses the data elements in that Data Set by referring to them in Merge Fields.