Once upon a time there was diff

The Unix world (GNU, Linux) was heavily based on text files
Text is always readable (it's friendly to men)
Text is accessible for impaired people (it's friendly to all men)
A simple editor can change any text file (it's friendly to machines)
ASCII text is portable (it's friendly to all machines)

History, at last, is validating our views:
All successful network protocols are text protocols
HTML is a text format
XML (depicted as the solution to all sins) is text
ODF is text (though embodied in a zip file)
With every task, with every data, people need to know
              what changes they accumulated while working
One of the first Unix programs was "diff"
Diff assumes that text files are line-oriented
The program reports to stdout the differences between two files
Differences are shown as a textual printout