17. A system comprising: a plurality of modules, each module comprising instructions retained on at least one machine-readable storage medium, that when executed by a machine perform identified operations, wherein the modules comprise: a file access module to access a main file name of a main file and to access a relationship definition associated with a package of data items, the relationship definition identifying a class of relationships between data items included in the package of data items, the relationship definition associating the main file with information stored in a related file, the at least one relationship definition including a template string and a first pattern string; and a matching module to determine whether a first portion of the main file name matches the first pattern string and, based on the determination, selectively to: match the main file name to the first pattern string; substitute a second substring of the main file name into the first pattern string; derive a second pattern string from the template string and the first pattern string having the substituted second substring of the main file name; and identify a related file name that matches the second pattern 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 without altering the information contained in the main file.
23. The system of claim 17 , wherein the template string includes a name portion symbol, the name portion symbol identifying a portion of the main file name, the matching module further, based on the determination, selectively to generate the second pattern string corresponding to the template string, the name portion symbol in the template string being replaced in the second pattern string by the portion of the main file name identified by the name portion symbol.