1. A document generation system for generating a customised document using content elements selected by rules operating on input information, the content elements comprising conditional and unconditional text elements, the system comprising: at least one computer having a document generation program installed thereon; wherein the system is capable of generating a fully or a partially customised document by evaluating the rules to select some of the content elements; and means adapted to generate a program structure representing the conditional text elements including space elements representing space characters, the evaluation of which determines the position of space characters inserted between the conditional text and unconditional text of the content elements.