an object inheriting from class "varFunc", representing a variance function structure.

an optional character string with a description of the varFunc class. Default depends on the method function:

for varComb:

"Combination of variance functions",

for varConstPower:

"Constant plus power of variance covariate",

for varConstProp:

"Constant plus proportion of variance covariate",

for varExp:

"Exponential of variance covariate",

for varIdent:

"Different standard deviations per stratum",

for varPower:

"Power of variance covariate",

for varFunc:

data.class(object).

some methods for this generic require additional arguments. None are used in this method.