Opens a Shiny dialog allowing the user to specify the content and chunk
options of a data chunk. As different dialog elements are specified, other
elements will be modified to suggest likely desired values. For example, if a
binary file is uploaded, then the format
will be set to binary
,
the encoding
will be set to base64
and the Encode data?
option will be checked. If these options are not appropriate, then they can
be altered afterwards.