In [BRS92] two important aspects of the structure of hyperdocuments are studied: hierarchies and metrics. Hierarchies are used to view a hyperdocument somewhat like a book with chapters, sections, subsections, etc. The hierarchical structure of a hyperdocument can be compared to the grid structure of a city, while the exceptions to the hierarchy: the cross-reference links, are the disturbing factors like Broadway is in Manhattan. If there are few cross-reference links, the user is not likely to get lost, as hierarchical document structures are common and resemble a book structure. Apart from the identification of hierarchies Botafogo, Rivlin and Shneiderman also studied a number of useful metrics, most importantly compactness and stratum, that measure how well-connected a hyperdocument is, and how "linear" its structure is. De Voght [DeVocht-94] ran a number of browsing experiments to find out how well a user will recognize the structure of a hyperdocument while browsing. These experiments of course depend on the browsing strategy of the user and on the navigation aids offered by the hypertext system, at least as much as on the actual structure of the hyperdocument.