Inline where inline_output_ok() allows it, and in its own iframe in any
other HTML (create_knitr_iframe()). A chart that cannot be shown inline
– an id the prefixing cannot scope, or any other error – is shown in an
iframe instead, with one warning per document: a failure never stops the
knit.
Usage
knitr_chart_output(content, options = list(), figure = FALSE)