Missing documentation for using Greasemonkey attributes in WebEngineScript

The documentation for WebEngineScript says, "The following Greasemonkey attributes are supported since Qt 5.8: @exclude, @include, @name, @match, and @run-at."

But there is no documentation about how to actually do it, and no examples I can find, for neither QML (which is what I'm interested in) nor C++. Where/how are we supposed to insert/apply Greasemonkey attributes?

Simply including the directives as comments inside the UserScript, like you would with Greasemonkey, has no effect.