a function or the name of a function. It determines how
    where the HTML code is directed to.
If the working environment is RStudio, the default value is
    "file.show". In other interactive environments it is
    "browser". In non-interactive sessions it is 
    "stdout".
If output equals "browser" the generated HTML code
    is shown using browseURL. If output
    equals "stdout" the HTML code is written to the console
    output window. If output equals "file.show", the
    function file.show is used.
If view_html is called within a Jupyter session,
    the HTML code created is envelopped in a pair of <div> tags
    and included into the Jupyter output.