knitr (version 1.33)

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()

Arguments

envirs

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

strict

Boolean; 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'.

Value

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

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://bookdown.org/yihui/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

# NOT RUN {
# 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()
# }