We introduce a simple and novel visual technique for the specification of context in structured documents called T-graphs that we base on T-configurations in document trees. The technique is implemented in the current version of D esigner. Although we are applying this technique in the specification of context-dependent style sheets for HTML, XML, and SGML documents, it is clear that it can be used in other environments such as query specification for structured documents and for computer program transformations. We compare T-graphs with the context specification techniques found in other style-sheet systems and we also provide examples of context that we can and cannot specify with T-graphs. Although T-graphs are restrictive, they lend themselves to visual construction and modification, our main requirement when we designed this context-specification method. We also investigate the time and space complexity of T-graph matching, a necessity for efficient implementation.