11. A computer-readable storage media encoded with a data structure for specifying a grammar for input parameters using a class, the data structure comprising: a class name for the class of an object, the class name identifying a command specified by a developer; definitional information of an expected parameter associated with the command, wherein the expected parameter is part of a parsable stream that includes an identifier associated with the command definitional information defining a grammar for the command; and a plurality of directives associated with the class, comprising: an interaction directive that determines a user interface for input of the expected parameter if the expected parameter is not entered at a command line; a document directive, that specifies textual information on the expected parameter when textual information on the expected parameter is requested, the textual information including a name to refer to an element in a command and a description of the elements; and a documentation directive that, when requested, generates textual information about the parameter, and provides a description of correct syntax when an invalid syntax is encountered, wherein: the class is derived from a base class, the base class comprising a plurality of categories of directives and one or more directives under each category of directives; and the plurality of directives of the class are either derived from the corresponding category of directives of the base class or extended by the developer of the command for the class.
11. A computer-readable storage media encoded with a data structure for specifying a grammar for input parameters using a class, the data structure comprising: a class name for the class of an object, the class name identifying a command specified by a developer; definitional information of an expected parameter associated with the command, wherein the expected parameter is part of a parsable stream that includes an identifier associated with the command definitional information defining a grammar for the command; and a plurality of directives associated with the class, comprising: an interaction directive that determines a user interface for input of the expected parameter if the expected parameter is not entered at a command line; a document directive, that specifies textual information on the expected parameter when textual information on the expected parameter is requested, the textual information including a name to refer to an element in a command and a description of the elements; and a documentation directive that, when requested, generates textual information about the parameter, and provides a description of correct syntax when an invalid syntax is encountered, wherein: the class is derived from a base class, the base class comprising a plurality of categories of directives and one or more directives under each category of directives; and the plurality of directives of the class are either derived from the corresponding category of directives of the base class or extended by the developer of the command for the class. 17. A computer-readable storage media of claim 11 , wherein the plurality of directives further includes a directive that specifies additional processing performed on the expected parameter.