numeric index or character key of entry in bib to open.
open.field
character vector of fields to use in bib to open
the BibEntry. Possible fields are any combination of “file”,
“url”, “eprint”, or “doi”. “eprint” is
implemented for eprinttype= “JSTOR”, “PubMed”,
or “arXiv”. When multiple fields are specified, they are tried in
the order they appear in the vector.
viewer
character string giving the name of the program to be used
as hypertext browser. It should be in the PATH, or a full path specified.
Alternatively, an R function to be called to invoke the browser. Defaults
to getOptions("pdfviewer") if open.field = "file" and
getOptions("browser"), otherwise.