The uptake in the software industry of notations for designing systems visually has been accelerated with the standardization of the Unified Modeling Language (UML). The formalization of diagrammatic notations is important for the development of essential tool support and to allow reasoning to take place at the diagrammatic level. Focusing on an extended version of Venn and Euler diagrams (which was developed to complement UML in the specification of software systems), this paper presents two levels of syntax for this system: type-syntax and token-syntax. Token-syntax is about particular diagrams instantiated on some physical medium, and type-syntax provides a formal definition with which a concrete representation of a diagram must comply. While these two levels of syntax are closely related to each other, the domains of type-syntax and token-syntax are ontologically independent from each other, that is, one is abstract and the other concrete. We discuss the roles of typesyntax and to...