This rule verifies files have a comment matching a given regular expression before the very first tag.
The header comment can be located before or after the <!DOCTYPE> declaration.
For example, with the format .*Copyright.*, the following code:
<html> <!-- Non-Compliant --> ... </html>
should be refactored into:
<!-- Copyright 2013 SonarSource SA --> <!-- Compliant --> <html> ... </html>