The core of Catalog data is in its "index". These methods get and set that slot.
index(x)
index(x) <- value
# S4 method for ShojiCatalog
index(x)
# S4 method for ShojiCatalog
index(x) <- value
a Catalog (VariableCatalog, Subvariables, or similar object)
For the setters, an appropriate-length list to assign
Getters return the list object in the "index" slot; setters
return x
duly modified.