The documentation at the top for this module does state that Java patterns should be used. But as a newcomer, it's confusing that the examples then shown are not in Java regex pattern form.

Update from maintainers:
https://github.com/checkstyle/checkstyle/blob/master/src/site/xdoc/checks/header/multifileregexpheader.xml

We need to use template file for this Check and convert all examples to be like in other Checks - executed by junit.
Example: https://github.com/checkstyle/checkstyle/tree/master/src/xdocs-examples/resources/com/puppycrawl/tools/checkstyle/checks/header/regexpheader
https://github.com/checkstyle/checkstyle/blob/master/src/xdocs-examples/java/com/puppycrawl/tools/checkstyle/checks/header/RegexpHeaderCheckExamplesTest.java