html4_document: HTML4 output format with CSS for Paged Media
In RLesur/weasydoc: Convert R Markdown to PDF Using HTML and CSS

This HTML format is developped only for bookdown.

html4_document(toc = FALSE, toc_depth = 3, number_sections = FALSE,
  fig_width = 5, fig_height = 4, fig_retina = 8, fig_caption = TRUE,
  dev = "png", dpi = 96, df_print = NULL, smart = TRUE,
  highlight = "default", math_engine = "webtex_svg", css = NULL,
  includes = NULL, keep_md = FALSE, self_contained = TRUE,
  md_extensions = NULL, pandoc_args = NULL)

`toc`	`TRUE` to include a table of contents in the output
`toc_depth`	Depth of headers to include in table of contents
`number_sections`	`TRUE` to number section headings
`fig_width`	Default width (in inches) for figures
`fig_height`	Default width (in inches) for figures
`fig_retina`	Setting this option to a ratio (for example, 2) will change the `dpi` parameter to `dpi * fig.retina`, and `fig_width` to `fig_width * dpi / fig_retina` internally; for example, the physical size of an image is doubled and its display size is halved when `fig_retina = 2`.
`fig_caption`	`TRUE` to render figures with captions
`dev`	Graphics device to use for figure output (defaults to png)
`dpi`	The DPI (dots per inch) for bitmap devices.
`df_print`	Method to be used for printing data frames. Valid values include `"default"`, `"kable"` and `"tibble"`. The `"default"` method uses `print.data.frame`. The `"kable"` method uses the `knitr::kable()` function. The `"tibble"` method uses the tibble::tibble-package to print a summary of the data frame. In addition to the named methods you can also pass an arbitrary function to be used for printing data frames. You can disable the `df_print` behavior entirely by setting the option `rmarkdown.df_print` to `FALSE`.
`smart`	Produce typographically correct output, converting straight quotes to curly quotes, — to em-dashes, – to en-dashes, and ... to ellipses.
`highlight`	Syntax highlighting style. Supported styles include "default", "tango", "pygments", "kate", "monochrome", "espresso", "zenburn", "haddock", and "textmate". Pass `NULL` to prevent syntax highlighting.
`math_engine`	Method to be used to render `TeX` math. Valid values include `"unicode"`, `"mathjax"`, `"mathml"`, `"webtex_svg"`, `"webtex_png"` and `"katex"`. See the pandoc manual for details.
`css`	One or more css files to include
`includes`	Named list of additional content to include within the document (typically created using the `includes` function).
`keep_md`	Keep the markdown file generated by knitting.
`self_contained`	Use `self_contained` to indicate if external dependencies are embedded in `HTML` file.
`md_extensions`	Markdown extensions to be added or removed from the default definition or R Markdown. See the `rmarkdown_format` for additional details.
`pandoc_args`	Additional command line options to pass to pandoc