Applies ROT-13 character rotation to the current selection, making it a little difficult to read. Applying ROT-13 again restores the original text.
Before the Internet went commercial, people had the good habit to use ROT-13 to conceal possible offensive postings in newsgroups and then add a warning message in plain text. This made sure that nobody would read the text by accident and be offended. If one was offended after applying ROT-13, he or she would only have himself or herself to blame for ignoring the warning.