Experiences with the use of the MSC language for complex system specifications have shown that certain extensions are necessary in order to arrive at sufficiently transparent and manageable descriptions. Extended HMSCs, where MSC reference symbols may either be presented by hypertext-like descriptions or, in an expanded form, as detailed MSCs, appear to be especially suitable for a compact and transparent MSC representation. For an effective usage of such advanced MSC constructs, a corresponding tool support seems to be mandatory where interactively the event structures of special paths can explicitly be expanded while others remain hidden as MSC references that contain solely textual descriptions. The name ‘HyperMSCs’ is proposed for such extended HMSCs. Beyond that, the communication between MSC references, operator expressions or HMSCs demands a generalisation of the gate concept. For that purpose, the introduction of MSC connectors denoting logical connections is suggested. MSC connectors may be expanded similar to MSC references. HyperMSCs enhanced by MSC connectors also provide a means for a selected visualisation of large MSCs in an interactive manner where, depending on the current selection, some parts are exhibited in full detail whereas other parts are presented in an abbreviated form. The same concepts may be applied for system modelling based on stepwise refinement starting with HyperMSCs, decomposed instances and MSC connector communication and for system testing.