The MIT, GPL, and Apache Licenses all make references to "files".
Here are example of such references: (all emphasis added)
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software...
For example, Corresponding Source includes interface definition files associated with source files for the work, and the source code for shared libraries and dynamically linked subprograms that the work is specifically designed to require, such as by intimate data communication or control flow between those subprograms and other parts of the work. ... If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.
"Source" form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files. ... You must cause any modified files to carry prominent notices stating that You changed the files ...
Is there a legal definition for what counts as a file, in the sense these licenses are using? Does something as small as a TCP packet count as a file? If not, where is the line? If I split a file from an open source project in two, is it the same file? What if I concatenate two of them together? In general, how much of a file's contents need to be modified before it counts as a distinct file?
Without some kind of legal definition, then it seems like there would be no way to definitively answer questions like "If use an MIT library in my project (by including the name and a version specifier in a package manager config file,) and I copy code from an example usage file distributed with the library, then modify it and add more of my own code, then distribute the resulting project (containing no more of the library author’s code but what remains of the example,) under MIT, do I need to include the original authors name in the copyright field?" without a court case.