tweak usecases object model per comments on pull #85
tweak usecases object model per comments on pull #85

cellml/libcellml,nickerso/libcellml,cellml/libcellml,MichaelClerx/libcellml,libcellml/buildbot-testing,hsorby/libcellml,hsorby/libcellml,nickerso/libcellml,nickerso/libcellml,cellml/libcellml,MichaelClerx/libcellml,hsorby/libcellml,nickerso/libcellml,MichaelClerx/libcellml,libcellml/buildbot-testing,cellml/libcellml,hsorby/libcellml