You can either select a PID/ID from the list or enter a valid PID/ID for resolving. Please notice that for DOI PID you could also ask for content including BibTeX, Citeproc JSON, RDF XML and RDF Turtle as per content negotiation. For this simply select an option under Resolving Mode.

This is a minimal UI for testing purposes. The full feature UI is located at PIDMR. The available PID providers and the possible queries can be found here: supported-pids