1. A computer-readable storage media having computer executable instructions, the instructions, when executed, performing a method comprising: receiving a parsable stream that includes an identifier associated with a command; retrieving definitional information based on the identifier that describes an expected parameter for the command; creating an object based on the definitional information; storing a parameter obtained from the parsable stream in the object in accordance with the definitional information associated with the expected parameter; applying a plurality of directives to the parsable stream, the plurality of directives comprising: a processing directive configured to manipulate the parameter before providing the object with the parameter to the command and includes specific size limits for strings and for collections that can be processed; 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; an interaction directive that determines a user interface for input of the expected parameter, wherein the interaction directive is applied if the expected parameter is not received in the parsable stream; and providing the object to the command, the object having a method invocable by the command, wherein: the definitional information and the plurality of directives are either derived from a reflection-based shell or extended by a developer of the command; the reflection-based shell provides one or more categories of directives and one or more directives under each category of directives; and the definition information and the plurality of directives associated with a first command are different from the definition information and the plurality of directives associated with a second command.