caT, a Petri net-based hypertext system, supports the modeling of user characteristics, contextual information, as well as the policies that govern the operation of a digital library within the infrastructure that presents its contents. Traditionally, users have created caT networks from scratch, thus limiting their use to small collections. In this research, we introduce TcAT, a new authoring tool that supports features for component-based authoring, with a view to enable the creation of large caT nets that can represent complex, real-life spaces such as libraries and museums. TcAT supports graphical, template-based creation of nets as well as a textual language for easy manipulation of large structures. It implements composition operations from Petri net theory to select, categorize, and modify existing net fragments as building blocks for composing larger networks. Authors may switch modes between visual and textual authoring at will, thus combining the strengths of expressing large nets textually and selecting net fragments via point-and-click interaction. A user evaluation of the new authoring mechanisms suggests that this is a promising tool for improving the efficiency of experienced users as well as that of novice users, who are unfamiliar with the Petri net formalism.