Effective comprehension of complex software systems requires understanding of both the individual documents that represent software and the complex relationships that exist within and between documents. Relationships of all kinds play a vital role in a software engineer's comprehension of, and navigation within and between, software documents. User-determined relationships have the additional role of enabling the engineer to create and maintain relational documentation that cannot be generated by tools or derived from other relationships. In this paper, we argue that for a software development environment to effectively support the understanding of complex software systems, relational navigation must be supported at both the document-focused (intra-document) and relation-focused (inter-document) levels. The need for a relation-focused approach is highlighted by an evaluation of an existing document-focused relational interface. This paper closes with the requirements for a relation-focused approach to relational navigation. These requirements focus on the user's perspective when interacting with a collection of related documents. This work defines the requirements for a software development environment that effectively supports the understanding of the software documents and relationships that define a complex software system.