query: character, search query. For more information on how to build a search query, see https://europepmc.org/Help
limit: integer, limit the number of records you wish to retrieve. By default, 25 are returned.
output: character, what kind of output should be returned. One of 'parsed', 'id_list' or 'raw' As default, parsed key metadata will be returned as data.frame. 'id_list returns a list of IDs and sources. Use 'raw' to get full metadata as list. Please be aware that these lists can become very large.