knitr (version 1.52)

render_html: Set or get output hooks for different output formats

Description

The render_*() functions set built-in output hooks for LaTeX, HTML, Markdown, reStructuredText, AsciiDoc, and Textile. The hooks_*() functions return a list of the output hooks for the corresponding format.

Usage

render_html()
hooks_html()
render_asciidoc()
hooks_asciidoc()
render_latex()
hooks_latex()
render_sweave()
hooks_sweave(envirs = c("Sinput", "Soutput", "Schunk"))
render_listings()
hooks_listings(envirs = c("Sinput", "Soutput", "Schunk"))
render_markdown(strict = FALSE, fence_char = "`")
hooks_markdown(strict = FALSE, fence_char = "`")
render_jekyll(highlight = c("pygments", "prettify", "none"), extra = "")
hooks_jekyll(highlight = c("pygments", "prettify", "none"), extra = "")
render_rst(strict = FALSE)
hooks_rst(strict = FALSE)
render_textile()
hooks_textile()
render_typst()
hooks_typst()

Value

NULL for render_* functions; corresponding hooks are set as a side effect. A list of output hooks for hooks_*()

functions.

Arguments

envirs

Names of LaTeX environments for code input, output, and chunk.

strict

Whether to use strict markdown or reST syntax. For markdown, if TRUE, code blocks will be indented by 4 spaces, otherwise they are put in fences made by three backticks. For reST, if TRUE, code is put under two colons and indented by 4 spaces, otherwise it is put under the sourcecode directive (this is useful for e.g., Sphinx).

fence_char

A single character to be used in the code blocks fence. This can be e.g. a backtick or a tilde, depending on your Markdown rendering engine.

highlight

Which code highlighting engine to use: if pygments, the Liquid syntax is used (default approach Jekyll); if prettify, the output is prepared for the JavaScript library prettify.js; if none, no highlighting engine will be used, and code blocks are simply indented by 4 spaces).

extra

Extra tags for the highlighting engine. For pygments, this can be 'linenos'; for prettify, it can be 'linenums'.

Details

There are three variants of Markdown documents: ordinary Markdown (render_markdown(strict = TRUE), which calls hooks_markdown(strict = TRUE)), extended Markdown (e.g., GitHub Flavored Markdown and Pandoc; render_markdown(strict = FALSE), which calls hooks_markdown(strict = FALSE)), and Jekyll (a blogging system on GitHub; render_jekyll(), which calls hooks_jekyll()).

For LaTeX output, there are three variants: knitr's default style (render_latex(), which calls hooks_latex() and uses the LaTeX framed package), Sweave style (render_sweave(), which calls hooks_sweave() and uses Sweave.sty), and listings style (render_listings(), which calls hooks_listings() and uses LaTeX listings package).

Default HTML output hooks are set by render_html() (which calls hooks_html()); render_rst() (which calls hooks_rst()) is for reStructuredText; render_textile() (which calls hooks_textile()) is for Textile, and render_asciidoc() (which calls hooks_asciidoc()) is AsciiDoc.

The render_*() functions can be used before knit() or in the first chunk of the input document (ideally this chunk has options include = FALSE and cache = FALSE) so that all the following chunks will be formatted as expected.

You can also use knit_hooks to set the format's hooks with the hooks_*() functions; see references for more info on further customizing output hooks.

References

See output hooks in https://yihui.org/knitr/hooks/, and some examples in https://pkg.yihui.org/rmarkdown-cookbook/output-hooks.html

Jekyll and Liquid: https://github.com/jekyll/jekyll/wiki/Liquid-Extensions; prettify.js: https://code.google.com/archive/p/google-code-prettify

Examples

# below is pretty much what knitr::render_markdown() does:
knitr::knit_hooks$set(knitr::hooks_markdown())

# you can retrieve a subset of the hooks and set them, e.g.,
knitr::knit_hooks$set(knitr::hooks_markdown()["source"])

knitr::knit_hooks$restore()