To run by command line

    vnu

To validate a file to an instance of the servlet (system tomcat, system jetty,
or vnu standalone server)

    vnu-client myFile.html

To run the standalone server

    vnu-server

To test a file which URL is on localhost (or 127.0.0.1 or alike), there are
two alternatives:

  - use your hostname instead of localhost.
  - use the 'nu.validator.servlet.allow-forbidden-hosts' Java system property

  See :
    - https://github.com/validator/validator/issues/1451#issuecomment-1290417602
    - https://github.com/validator/validator/issues/1477#issuecomment-3688500565