When the output format is HTML, include_url() inserts an iframe in the
output; otherwise it takes a screenshot of the URL and insert the image in
the output. include_app() takes the URL of a Shiny app and adds
?showcase=0 to it (to disable the showcase mode), then passes the URL
to include_url().
include_url(url, height = "400px")include_app(url, height = "400px")
a character string of a URL
the height of the iframe
An R object with a special class that knitr recognizes internally to generate the iframe or screenshot.