A path to a .csv file.
Should warnings be emitted, if the type of file cannot be determined?
When attempting to re-import, a heuristic is applied. If the file has column
names which match the names from any of the
find_* functions, the file
is read with the corresponding specifications. If no column names are
recognized, files are recognized based on the number of columns. Since both
references and footnotes have only two columns, the first line is inspected
In case there is still no match, the file is read with
guess_max = 5000 and a warning is raised.