The invention provides a document generation system for generating a customized document using content elements selected by rules operating on input information, the operating information comprising transaction values. The system comprises at least one computer having a document generation program stored thereon, means to associate further rules with the transaction values, and means to evaluate said further rules to produce an indication of the relevance of the presence or absence of the transaction values in a fully or partially customized generated document. The effect of the transaction values is represented by means of a mark-up.