language-class
(Package: methods) :
Classes to Represent Unevaluated Language Objects
The virtual class "language" and the specific classes that extend it represent unevaluated objects, as produced for example by the parser or by functions such as quote.
The functions below produce the package associated with a particular environment or position on the search list, or of the package containing a particular function. They are primarily used to support computations that need to differentiate objects on multiple packages.
The “...” argument in R functions is treated specially, in that it matches zero, one or more actual arguments (and so, objects). A mechanism has been added to R to allow “...” as the signature of a generic function. Methods defined for such functions will be selected and called when all the arguments matching “...” are from the specified class or from some subclass of that class.
S3Part
(Package: methods) :
S3-style Objects and S4-class Objects
Old-style (S3) classes may be registered as S4 classes (by calling setOldClass), and many have been. These classes can then be contained in (that is, superclasses of) regular S4 classes, allowing formal methods and slots to be added to the S3 behavior. The function S3Part extracts or replaces the S3 part of such an object. S3Class extracts or replaces the S3-style class. S3Class also applies to object from an S4 class with S3methods=TRUE in the call to setClass.
These are the objects that hold the definition of classes of objects. They are constructed and stored as meta-data by calls to the function setClass. Don't manipulate them directly, except perhaps to look at individual slots.
getMethod
(Package: methods) :
Get or Test for the Definition of a Method
Functions to look for a method corresponding to a given generic function and signature. The functions getMethod and selectMethod return the method; the functions existsMethod and hasMethod test for its existence. In both cases the first function only gets direct definitions and the second uses inheritance. In all cases, the search is in the generic function itself or in the package/environment specified by argument where.
The arguments to function new to create an object from a particular class can be interpreted specially for that class, by the definition of a method for function initialize for the class. This documentation describes some existing methods, and also outlines how to write new ones.
representation
(Package: methods) :
Construct a Representation or a Prototype for a Class Definition
These are old utility functions to construct, respectively a list designed to represent the slots and superclasses and a list of prototype specifications. The representation() function is no longer useful, since the arguments slots and contains to setClass are now recommended.
Documentation
(Package: methods) :
Using and Creating On-line Documentation for Classes and
Special documentation can be supplied to describe the classes and methods that are created by the software in the methods package. Techniques to access this documentation and to create it in R help files are described here.
providing 
.