a non-empty character string giving the URL to be loaded.
Some platforms also accept file paths.
a non-empty character string giving the name of the
program to be used as the HTML browser. It should be in the PATH,
or a full path specified. Alternatively, an R function to be
called to invoke the browser.
Under Windows NULL is also allowed (and is the default), and
implies that the file association mechanism will be used.
Should the URL be encoded by
URLencode before passing to the browser? This is not
needed (and might be harmful) if the browser program/function
itself does encoding, and can be harmful for file:// URLs on some
systems and for http:// URLs passed to some CGI applications.
Fortunately, most URLs do not need encoding.
Which URL schemes are accepted is platform-specific: expect
http://, https:// and ftp:// to work, but
mailto: may or may not (and if it does may not use the user's
preferred email client).
For the file:// scheme the format accepted (if any) can depend on
both browser and OS.
The default browser is set by option "browser", in turn set by
the environment variable R_BROWSER if that is set, otherwise to
To suppress showing URLs altogether, use the value "false".
Some browsers have required : be replaced by | in file
paths: others do not accept that. All seem to accept \ as a
path separator even though the RFC1738 standard requires /.
To suppress showing URLs altogether, set browser = "false".