Get a data-flow node where this value leaves the current codebase and flows into an external library (or in general, any external codebase).
Concretely, this is either an argument passed to a call to external code, or the right-hand side of a property write on an object flowing into such a call.
For example:
// 'x' is matched by API::moduleImport("foo").getParameter(0).asSink()
require('foo')(x);
// 'x' is matched by API::moduleImport("foo").getParameter(0).getMember("prop").asSink()
require('foo')({
prop: x
});