The core of Catalog data is in its "index". These methods get and set that slot.
index(x)
index(x) <- value
# S4 method for class 'ShojiCatalog'
index(x)
# S4 method for class 'ShojiCatalog'
index(x) <- valueGetters return the list object in the "index" slot; setters
return x duly modified.