opts_knitlist of length 4.opts_knit$set()), we can also set package
options prior to loading knitr or calling knit() using
options() in base R. A global option knitr.package.foo
in options() will be set as an option foo in opts_knit,
i.e. global options in base R with the prefix knitr.package.
correspond to options in opts_knit. This can be useful to set package
options in Below is a list of default package options, retrieved via
opts_knit$get():
A list of available options: