1. A computer-readable medium having instructions stored thereon that, when executed by a processor, cause the processor to implement a plug-in system, the instructions comprising: invoking a plug-in framework within a plug-in, wherein the plug-in framework comprises a software library configured to define, register, and configure plug-ins, wherein the plug-in comprises a software module that extends or customizes functionality of a software application that is external to the plug-in, and wherein the plug-in comprises a mapping name; searching a plug-in instance declaration, by the plug-in framework, for a mapping that comprises the mapping name, wherein the plug-in instance declaration is located within a plug-in file, and wherein the plug-in declaration comprises one or more mappings; and when a mapping that comprises the mapping name is found, returning a value, by the plug-in framework, to the plug-in based on the mapping.