This paper discusses the requirements for authoring methodologies for large multimedia systems to be used for technical documentation in the domain of 'safety critical' industries. In such industries, the documentation used to support maintenance and repair may itself be safety critical, in that incorrect documentation can lead to incorrect maintenance procedures. Design issues for such systems include those of the verifiable, in terms of both their content and other issues such as sequence of presentation. It is argued that the addressing of these issues is essential to the development of technical documentation systems that are of sufficient quality to be used for safety critical applications such a within the transport industry. The requirements that viable design methodologies for these applications must address are discussed, and a methodology is proposed, based on traditional authoring methods and process algebra based formal specification and verification.