Function to turn the parsed response document into meaningful data.
It must accept one argument, doc, the parsed response document.
The return value must be compatible with vctrs::list_unchop(),
e.g. a vector, list, or data frame.
Details
API results are parsed based on the retmode parameter. XML documents will
be parsed into xml2::xml_document objects and an error will be raised if
it contains an <ERROR> node.
Builtin processors can be referred to by name instead of specifying your own function. Some helpers provide additional processors, but these are always available:
"identity": Puts the parsed output document into a list. Where multiple requests are made (e.g. using the batched APIs likeefetch()) these will then be concatenated into a single list.