Instructions to tenderers expand on the basic information contained in the invitation to tender. These instructions communicate to contractors the technicalities of the tendering process. Although they repeat some of the information contained in the invitation to tender, they also provide information on such matters as modification of tenders once submitted prior to opening, alterations to the tender, tender withdrawals, tender rejections, performance guarantees, methods for handling alternative proposals and order of precedence in the case of discrepancies between numbers and words. The American Institute of Architects (1997b) has prepared a standard document entitled Instructions to Bidders, often used in the tendering process for private projects. However, because these are general instructions, they usually must be modified through issuance of supplementary instructions. Some public agencies in the USA have adopted this document as well and they provide additions, deletions and amendments as part of their agency instructions common to all projects.