This reads in a xml document and gets all the derivations/comments. These can be cross referenced to variables using the derivation_id's
xml_to_derivations(doc)xml document
dataframe with derivation id's and derivations
Other xml builder:
xml_to_codelist(),
xml_to_ds_spec(),
xml_to_ds_vars(),
xml_to_value_spec(),
xml_to_var_spec()