30. A machine-readable storage medium embodying instructions which, when executed by a machine, cause the machine to perform operations comprising: accessing a relationship definition file having at least one relationship definition associated with a package of data items, the at least one relationship definition identifying a class of relationships between data items included in the package of data items, the at least one relationship definition associating a main file with information stored in a related file, the at least one relationship definition including a template string and a first pattern string; accessing a main file name of the main file; matching the main file name to the first pattern string; and deriving a second pattern string from the template string, wherein the information stored in the related file is related to information contained in the main file, and wherein the information stored in the related file is for use in rendering the main file, by an electronic document rendering application, without altering the information contained in the main file.
30. A machine-readable storage medium embodying instructions which, when executed by a machine, cause the machine to perform operations comprising: accessing a relationship definition file having at least one relationship definition associated with a package of data items, the at least one relationship definition identifying a class of relationships between data items included in the package of data items, the at least one relationship definition associating a main file with information stored in a related file, the at least one relationship definition including a template string and a first pattern string; accessing a main file name of the main file; matching the main file name to the first pattern string; and deriving a second pattern string from the template string, wherein the information stored in the related file is related to information contained in the main file, and wherein the information stored in the related file is for use in rendering the main file, by an electronic document rendering application, without altering the information contained in the main file. 31. The machine-readable storage medium of claim 30 , wherein accessing the related file comprises: substituting a substring of the main file name for a first wildcard symbol in a first pattern string; and substituting the first pattern string with the substring of the main file name for a wildcard-identifying symbol of the template string, to generate the related file name.