Opens an HTML document using the OS default HTML browser. Note that this
 call is dependent on the operating system (currently only Windows and
 Unix are supported).
 The document given by query can either be a local file or a
 web page. If the query was given as non-url string, i.e. as a
 standard file pathname, the method will automatically check if the
 file exists and conform the query to a correct url starting with
 file:. The used url will be returned as a string.
Any suggestion how implement this on Apple system are welcome!
## Static method (use this):
## System$openBrowser(query, ...)## Don't use the below:
# S3 method for System
openBrowser(this, query, ...)
The path to document to be opened by the browser.
Returns the url of the query.
It is hard to create a good cross-platform openBrowser() method,
  but here is one try.
In the following text <browser> is the value returned by
  getOption("browser") and <url> is the URL conformed
  query, which starts with either file: or http:.
On a Windows system, if <browser> is not NULL,
  first
shell.exec(<browser> <url>)
is tried. If this fails, then
shell.exec(<url>)
is tried. Using this latter approach will not guarantee that
  an HTML browser will open the url, e.g. depending on the Windows file
  associations, a *.txt file might be opened by NotePad. However,
  it will most likely open something.
  If <browser> contains spaces, make sure it is quoted.
On Unix systems, system() will be used to call:
 <browser> -remote "openURL(<url>)" 2> /dev/null || <browser> <url> &
For more information see System.
# NOT RUN {
  System$openBrowser("http://www.r-project.org/")
# }
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