Litedown

https://yihui.org/litedown/
Admin
Litedown is a lightweight R Markdown alternative that creates HTML and LaTeX output with minimal...
Tokens:32,913
Snippets:503
Trust Score:9.8
Update:6 months ago
Show doc for...
Tokens:
Raw
### Graphics device examples

Source: https://yihui.org/litedown

Examples showing how to set resolution and background color for plots using dev.args.

```r
```{r}
#| chunk-a, dev.args = list(res = 96),
#| fig.alt = 'png with a resolution of 96 ppi'

plot(cars)
```
```

```r
```{r}
#| chunk-b, dev = 'svg', dev.args = list(bg = 'lightyellow'),
#| fig.alt = 'svg with a lightyellow background'

plot(cars)
```
```

--------------------------------

### Install litedown and xfun Packages

Source: https://yihui.org/litedown

Install the litedown and xfun packages from the yihui R-universe repository. This is the recommended method for users wishing to try the experimental litedown package.

```bash
install.packages(c('litedown', 'xfun'), repos = 'https://yihui.r-universe.dev')
```

--------------------------------

### Launch Live Preview

Source: https://yihui.org/litedown

Starts a file browser to preview renderable files in the current directory.

```R
litedown::roam()
```

--------------------------------

### Configure Prism.js syntax highlighting

Source: https://yihui.org/litedown

Example configuration for using Prism.js with specific styles and languages.

```yaml
js_highlight:
  package: prism
  style: dark
  languages: [r, latex, yaml]
```

--------------------------------

### Configure MathJax and KaTeX rendering

Source: https://yihui.org/litedown

Examples of specifying math rendering libraries, versions, and custom files.

```yaml
js_math:
  package: mathjax
  version: 3
  js: es5/tex-chtml.js
```

```yaml
js_math:
  package: mathjax
  version: 2
  js: MathJax.js?config=TeX-AMS-MML_CHTML
```

```yaml
js_math:
  package: katex
  version: 0.16.4
  js: [dist/katex.min.js, dist/contrib/mhchem.min.js]
```

--------------------------------

### Launch Live Preview

Source: https://yihui.org/litedown

Starts the litedown live preview server. Use the live argument to toggle automatic refreshing.

```R
litedown::roam()
```

```R
litedown::roam(live = FALSE)
```

--------------------------------

### BibTeX Entry Example

Source: https://yihui.org/litedown

An example of a BibTeX entry for a manual, including title, author, organization, address, year, and URL. Keywords must be alphanumeric or hyphens.

```bibtex
@Manual{R-base,
  title = {R: A Language and Environment for Statistical Computing},
  author = {{R Core Team}},
  organization = {R Foundation for Statistical Computing},
  address = {Vienna, Austria},
  year = {2024},
  url = {https://www.R-project.org/},
}
```

--------------------------------

### Include Arbitrary CSS and JS Libraries

Source: https://yihui.org/litedown

Example of integrating the simple-datatables library into a document.

```yaml
---
title: Display Tables with the JS Library DataTables
output:
  html:
    meta:
      css: ["@default", "@npm/simple-datatables/dist/style"]
      js: ["@npm/simple-datatables"]
---

::: {#mtcars-table}
```{r}
I(mtcars)
```
:::

```{js, type = "module"}
new simpleDatatables.DataTable('#mtcars-table > table');
```
```

--------------------------------

### Table caption and environment configuration

Source: https://yihui.org/litedown

Example of using tab.cap and tab.env chunk options to customize table output.

```r
#| simple, tab.cap = 'First 3 rows of the `cars` data.',
head(cars, 3)
```

--------------------------------

### Convert Fenced Div to HTML

Source: https://yihui.org/litedown

Example of the resulting HTML output for a fenced Div.

```html
<div class="foo" id="bar" style="color: red;">
</div>
```

--------------------------------

### Inline Code Syntax Examples

Source: https://yihui.org/litedown

Demonstrates standard inline code syntax, handling nested backticks, and providing chunk options.

```markdown
`{r} paste("`", rnorm(1), "`")`
```

```markdown
`` `{lang} code` ``
```

```markdown
`{r, eval = FALSE} code`
```

--------------------------------

### LaTeX Environment Output

Source: https://yihui.org/litedown

The resulting LaTeX code for the provided fenced Div examples.

```latex
\begin{tiny}
This is \emph{tiny} text.
\end{tiny}
```

```latex
\begin{minipage}{.5\linewidth}
```

--------------------------------

### R Output Console Display

Source: https://yihui.org/litedown

The resulting output from the numeric calculation example.

```text
#> [1] "1.234568"          "123456.789000"     "-1234567.890000"  
#> [4] "1234567890.000000" "0.000001"
```

--------------------------------

### Generate Tabsets from Configuration

Source: https://yihui.org/litedown

Utilize the `xfun::tabset()` function with a configuration object to programmatically create tabsets. This example shows its use with a YAML file.

```r
cfg = xfun::taml_file('_litedown.yml')
xfun::tabset(cfg, dput)

```

--------------------------------

### Configure Working Directory via Chunk Options

Source: https://yihui.org/litedown

Examples of setting the working directory relative to the input file or as an absolute path using the 'wd' chunk option.

```text
wd = '../'
```

```text
wd = 'C:/Documents/Project/'
```

--------------------------------

### Create a Custom Example Callout

Source: https://yihui.org/litedown

Define a callout with the `callout-example` class and use the `data-legend` attribute to set a custom title for the callout.

```markdown
::: {.callout-example data-legend="Demo"}
Change the title of this example to "Demo".
:::
```

--------------------------------

### Ordered List Markdown Examples

Source: https://yihui.org/litedown

Demonstrates equivalent ordered list syntaxes in Markdown. The numbering of the first item dictates the sequence, and subsequent numbers can be arbitrary.

```markdown
1. Get up!
1. Write a book!
1. Go to bed!
```

```markdown
1. Get up!
2. Write a book!
3. Go to bed!
```

```markdown
5. Get up!
100. Write a book!
1. Go to bed!
```

```markdown
5. Get up!
6. Write a book!
7. Go to bed!
```

--------------------------------

### Get Package Manual Pages with pkg_manual()

Source: https://yihui.org/litedown

Use pkg_manual() to list all available manual pages for the R package. This function requires no arguments.

```r
litedown::pkg_manual()
```

--------------------------------

### Inline Numeric Formatting Examples

Source: https://yihui.org/litedown

Demonstrates the use of inline R expressions for numeric output and the application of formatting options like 'signif' and 'power'.

```markdown
---
title: Inline output
---

We know that $\pi = `{r} pi`$, and the first 3 letters are `{r} LETTERS[1:3]`. The first 3 variables of `mtcars` are `{r} xfun::join_words(names(mtcars)[1:3])`. You will not see this value `{r, eval = FALSE} 2 * pi`.

Some numbers:

```{r}
x = 1.23456789 * 10^c(0, 5, 6, 9, -6) * c(1, 1, -1, 1, 1)
sprintf('%f', x)
```

| n = signif/p = power | n = 3, p = 6 | n = 5/2/4/1/7 | p = 0/4/Inf/9/5 |
|-----------|-----------:|---------------------:|----------------------:|
| x_1       | `{r} x[1]` | `{r, signif=5} x[1]` | `{r, power=0}   x[1]` | 
| x_2 10^5  | `{r} x[2]` | `{r, signif=2} x[2]` | `{r, power=4}   x[2]` |
| x_3 10^6  | `{r} x[3]` | `{r, signif=4} x[3]` | `{r, power=Inf} x[3]` |
| x_4 10^9  | `{r} x[4]` | `{r, signif=1} x[4]` | `{r, power=9}   x[4]` |
| x_5 10^-6 | `{r} x[5]` | `{r, signif=7} x[5]` | `{r, power=5}   x[5]` |

An equation: $Y = 300 `{r, dollar = FALSE, signif = 1} x[3]`x$.
```

--------------------------------

### Managing Chunk Options with reactor()

Source: https://yihui.org/litedown

Demonstrates getting and setting global chunk options using `litedown::reactor()`. Options set here can be overridden by chunk-specific settings.

```r
opts = litedown::reactor()
opts$fig.width  # get an option
opts$echo = FALSE  # set an option via assignment
```

--------------------------------

### Minimal Litedown Source Example

Source: https://yihui.org/litedown

A basic document structure demonstrating code chunks and inline R expressions that are processed by fuse().

```markdown
---
title: Area of a circle
---

Define the radius as `x`:

```{r}
x = 1 + 1
```

When the radius is `{r} x`, the area will be `{r} pi * x^2`.
```

```markdown
---
title: Area of a circle
---

Define the radius as `x`:

``` {.r}
x = 1 + 1
```

When the radius is 2, the area will be 12.6.
```

--------------------------------

### Example Computational Document Structure

Source: https://yihui.org/litedown

A demonstration of a document containing YAML metadata, code chunks, and inline R code expressions.

```markdown
---
title: "A Report on the Wall"
author: "`{r} who`"
date: "`{r} Sys.Date()`"
---

```{r, order = 0}
who = 'Humpty Dumpty'
```

`{r} who` sat on a wall.

`{r} who` had a great fall.

```{r}
broken = strsplit(who, ' ') |> unlist()
```

All the king's horses and all the king's men

Couldn't put `{r} broken[1]` together again.

<!--
If the king's horses and men knew R, they could've put
Humpty together again by paste(broken, collapse = ' ').
-->
```

--------------------------------

### JavaScript Ternary Operator Example

Source: https://yihui.org/litedown

A concise JavaScript example demonstrating the ternary operator for conditional assignment. This is useful for simple if-else logic.

```js
x < 0 ? -x : x;
```

--------------------------------

### Basic R expression evaluation

Source: https://yihui.org/litedown

A simple R expression example showing output capture.

```r
1 + 1
```

--------------------------------

### Load rbibutils Package

Source: https://yihui.org/litedown

Ensure the `rbibutils` package is installed and loaded for citation management functionality in litedown.

```r
xfun::pkg_load2("rbibutils")
```

--------------------------------

### Configure Figure Decoration in R Markdown

Source: https://yihui.org/litedown

Examples of using chunk options to control figure layout, captions, and dimensions.

```r
---
title: Decorating figures
output:
  html:
    meta:
      css: ["@default", "@article"]
      js: ["@sidenotes"]
---

Place two plots side by side via the `width` attribute:

```{r}
#| chunk-a, attr.plot = 'width="45%"',
#| fig.alt = c('a histogram', 'a sunflower plot'),
#| fig.cap = 'Exploring the faithful dataset.',

hist(faithful$eruptions, main = '', border = 'white')
sunflowerplot(faithful)
```

A full-width figure (requires the `@article` CSS):

```{r}
#| chunk-b, fig.dim = c(14, 4), fig.env = '.figure .fullwidth',
#| fig.cap = 'Monthly mean relative sunspot numbers from 1749 to 1983.'
par(mar = c(4, 4, .1, .1), bg = 'lightyellow', fg = 'red', las = 1)
plot(sunspots, col = 'red')
grid()
```
```

--------------------------------

### Configure Right-Aligned Quote Footer

Source: https://yihui.org/litedown

Enable right-alignment for blockquote footers starting with an em-dash.

```yaml
js: ["@right-quote"]
```

--------------------------------

### Configure Plot Device and Dimensions

Source: https://yihui.org/litedown

Examples of setting plot file extensions, dimensions, and output paths using chunk options.

```r
```{r, chunk-a, dev = 'jpeg', fig.ext = '.jpg'}
plot(cars)
```
```

```r
```{r, chunk-b, fig.dim = c(5, 4)}
plot(cars)
```
```

```r
```{r, chunk-c, fig.path = 'figures/'}
plot(cars)
```
```

--------------------------------

### Configure chunk attributes with attr.* options

Source: https://yihui.org/litedown

Example demonstrating the use of attr.chunk, attr.source, and attr.plot to apply custom classes and attributes to chunk elements.

```markdown
---
title: The `attr.*` chunk options
---

1. Add an ID `#example-a` to the whole chunk.

2. Add line numbers to source blocks via the `.line-numbers` class.

3. Add the class `.round` to the first plot and set its width to 400px.

4. Add two classes `.dark` and `.img-center` to the second plot.

```{r}
#| example-a,
#| attr.chunk = '#example-a',
#| attr.source = '.r .line-numbers',
#| attr.plot = c('.round width="400"', '.dark .img-center'),
#| fig.alt = c('A scatterplot of rnorm(100) numbers.',
#|   'A sunflower plot of iris.')

plot(rnorm(100), rnorm(100))
i34 = iris[, 3:4]
smoothScatter(i34)
sunflowerplot(i34, add = TRUE)
```

Define CSS rules for the classes in the `#example-a` chunk:

```{css}
#example-a {
  .round { border: solid 1px; border-radius: 50%; }
  .dark  { filter: invert(1); }
  .img-center { display: block; margin: auto; }
}
```

--------------------------------

### Configure caption positions

Source: https://yihui.org/litedown

A full document example showing how to toggle between top and bottom positions for figure and table captions.

```markdown
---
title: Caption position
---

## Default caption positions

```{r, fig-bottom, fig.cap = 'Bottom figure caption.'}
plot(cars)
```

```{r, tab-top, tab.cap = 'Top table caption.'}
cars
```

## Change the positions

```{r, fig-top, fig.cap = 'Top figure caption.', cap.pos = 'top'}
plot(cars)
```

```{r, tab-bottom, tab.cap = 'Bottom table caption.', cap.pos = 'bottom'}
cars
```
```

--------------------------------

### Get Package Description with pkg_desc()

Source: https://yihui.org/litedown

Use pkg_desc() to retrieve the description of the R package. This function requires no arguments.

```r
litedown::pkg_desc()
```

--------------------------------

### TAML Data Types Example

Source: https://yihui.org/litedown

Demonstrates the supported data types in TAML, including scalars, null values, expressions, and vectors.

```yaml
a: 1
b: "string"
c: true
d: null
# e is also null
e:
# an expression
f: !expr 1 + 1
# vectors
g: [1, 2, 3]
h: ["foo", "bar"]
```

--------------------------------

### Get commonmark Arguments and Extensions

Source: https://yihui.org/litedown

Retrieves the formal arguments for `commonmark::markdown_html` and lists available commonmark extensions.

```r
# commonmark's arguments
opts = formals(commonmark::markdown_html)
opts = opts[setdiff(names(opts), c('text', 'extensions'))]
unlist(opts)
#> hardbreaks      smart  normalize  sourcepos  footnotes 
#>      FALSE      FALSE      FALSE      FALSE      FALSE 
# commonmark's extensions
commonmark::list_extensions()
#> [1] "table"         "strikethrough" "autolink"      "tagfilter"    
#> [5] "tasklist"     

```

--------------------------------

### Custom execution order for text and code chunks

Source: https://yihui.org/litedown

This example demonstrates how to use the `order` option to control execution flow. The first text chunk is executed last (`order = N + 1`) to ensure variables from later chunks are available. The last code chunk is moved earlier (`order = i - 1.5`) so its result is ready for a preceding text chunk.

```markdown
---
title: Custom execution order
abstract: "We analyzed `{r, order = N + 1} nrow(x)` `{r} n_cyl`-cylinder cars, with an average MPG of `{r} m`."
---

Subset the data:

```{r}
n_cyl = 8
x = subset(mtcars, cyl == n_cyl)
```

The average MPG `{r} m` is calculated from:

```{r, order = i - 1.5}
m = mean(x$mpg)
```


```

```markdown
---
title: Custom execution order
abstract: "We analyzed 14 8-cylinder cars, with an average MPG of 15.1."
---

Subset the data:

``` {.r}
n_cyl = 8
x = subset(mtcars, cyl == n_cyl)
```

The average MPG 15.1 is calculated from:

``` {.r}
m = mean(x$mpg)
```


```

--------------------------------

### R Code Example for Floating Point Comparison

Source: https://yihui.org/litedown

This R code demonstrates a comparison of floating-point numbers, highlighting potential issues with strict equality checks.

```r
seq(0, 1, .2) == c(0, .2, .4, .6, .8, 1)
```

--------------------------------

### Simple HTML Template Example

Source: https://yihui.org/litedown

A basic HTML template structure with placeholders for title and body content. Variables like `$title$` and `$body$` are substituted during document generation.

```html
<html>
  <head>
    <title>$title$</title>
  </head>

  <body>
  $body$
  </body>
</html>

```

--------------------------------

### TAML Specification Example

Source: https://yihui.org/litedown

Illustrates the basic structure of TAML, including nested fields and various data types like numbers, strings, booleans, and vectors. Values can be quoted or unquoted based on interpretation.

```taml
i:
  i1: -1e8
  i2: "another string"
  i3:
    i31: [true, false, true]
any_character.is-okay: string not quoted
```

--------------------------------

### Get Package News with pkg_news()

Source: https://yihui.org/litedown

Use pkg_news() to retrieve the news or changelog for the R package. Set recent = 0 to show the full news history.

```r
litedown::pkg_news(recent = 0)  # show full news
```

--------------------------------

### Use the code chunk option

Source: https://yihui.org/litedown

Demonstrates generating code dynamically using the code option with sprintf.

```markdown
---
title: The `code` option
---

Define a code template `tpl`:

```{r}
tpl    = 'lm(mpg ~ %s, data = mtcars) |> summary() |> coef()'
x_vars = names(mtcars)[2:4]
```

We run regressions on three variables one by one:

```{r, code = sprintf(tpl, x_vars)}
```
```

--------------------------------

### Configure HTML Slides

Source: https://yihui.org/litedown

Enable slide functionality using snap.css and snap.js.

```yaml
css: ["@default", "@snap"]
js: ["@snap"]
```

--------------------------------

### GitHub Workflow for Deploying Package Site

Source: https://yihui.org/litedown

This workflow automates the building and deployment of a litedown package site to GitHub Pages. It checks out the code, sets up R and dependencies, uses the litedown/site action, uploads the site artifact, and deploys it.

```yaml
name: Build and deploy package site

on:
  push:
    branches: ["main"]

permissions:
  contents: read
  pages: write
  id-token: write

jobs:
  deploy:
    environment:
      name: github-pages
      url: ${{ steps.deployment.outputs.page_url }}
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@HEAD
      - uses: actions/configure-pages@HEAD
        with:
          enablement: true
      - uses: r-lib/actions/setup-r@HEAD
        with:
          use-public-rspm: true
      - uses: yihui/actions/setup-r-dependencies@HEAD
      - uses: yihui/litedown/site@HEAD
        with:
          site-dir: 'site'
      - uses: actions/upload-pages-artifact@HEAD
        with:
          path: 'site'
      - id: deployment
        uses: actions/deploy-pages@HEAD

```

--------------------------------

### Define website configuration

Source: https://yihui.org/litedown

Configure website rebuild behavior and HTML metadata like CSS and navigation headers/footers.

```yaml
site:
  rebuild: "outdated"
  pattern: "[.]R?md$"

output:
  html:
    meta:
      css: ["@default"]
      include_before: "[Home](/) [About](/about.html)"
      include_after: "&copy; 2024 | [Edit]($input$)"

```

--------------------------------

### Get or set language engine

Source: https://yihui.org/litedown

Retrieve an engine definition or register a new one using a function.

```r
litedown::engines('md')
```

```r
litedown::engines(LANG = function(x, inline = FALSE, ...) {

})
```

--------------------------------

### Configure Book CSS

Source: https://yihui.org/litedown

Apply book-specific styling to the document.

```yaml
css: ["@book"]
```

--------------------------------

### Define a footnote

Source: https://yihui.org/litedown

Use the [^n] syntax to reference a footnote and define its content in a separate block starting with [^n]:.

```markdown
Insert a footnote here.[^1]

[^1]: This is the footnote.
```

--------------------------------

### Identify invalid LaTeX math syntax

Source: https://yihui.org/litedown

Examples of common syntax errors that prevent LaTeX math from being correctly parsed.

```markdown
$ x + y$  <- space after the opening `$`
text$x + y$  <- lack of space before the opening `$`
text $x + y$10 text  <- number after closing `$`
$x +
y$  <- multi-line `$ $` expressions
$`x + y`$  <- expression wrapped in backticks

$$x +
  y
$$
^- lack of non-space character before closing `$$`
```

--------------------------------

### Verbosity levels in R chunks

Source: https://yihui.org/litedown

Examples demonstrating how the verbose chunk option affects the printing of invisible R values.

```r
1:5
#> [1] 1 2 3 4 5
x = 1 + 1
y = x^2
```

```r
1:5
#> [1] 1 2 3 4 5
x = 1 + 1
y = x^2
#> [1] 4
```

```r
1:5
#> [1] 1 2 3 4 5
x = 1 + 1
#> [1] 2
y = x^2
#> [1] 4
```

--------------------------------

### Configure Keyboard Shortcut Styling

Source: https://yihui.org/litedown

Enable styling for keyboard shortcut elements.

```yaml
css: ["@key-buttons"]
js: ["@key-buttons"]
```

--------------------------------

### Configure print options for objects

Source: https://yihui.org/litedown

Demonstrates using base::print() with specific arguments for table and factor classes.

```R
---
title: Print objects
---

Print objects with `base::print()`, and use different arguments for different objects.

```{r}
#| print = NA,
#| print.args = list(table = list(zero.print = '.'),
#|   factor = list(quote = TRUE, max.levels = 3))

X = c('a', 'b', 'c', 'c', 'c', 'a')
Y = factor(c('A', 'B', 'C', 'C', 'D', 'E'))
Y  # factor

table(X, Y)  # table
```
```

```R
table(X, Y)  # table
```

--------------------------------

### Create a multi-paragraph block quote

Source: https://yihui.org/litedown

Use the > character at the start of each line to define a block quote containing multiple paragraphs.

```markdown
> "You're an oaf. I told you quite distinctly to make his discharge papers out."
>
> And all the bile which had accumulated in the judge advocate's soul in the course of that day because of Captain Linhart and Švejk poured out like a wild torrent on the head of the staff warder. At the end of it Bernis said:
>
> "And now do you understand that you are a prize royal oaf?"
>
> This is something which should only be said to kings and emperors, but even this simple staff warder, who was no royal personage, was not very pleased about it.
>
> ---Jaroslav Hašek, _The Good Soldier Švejk_ (Chapter 9)
```

--------------------------------

### Get Package Citation with pkg_citation()

Source: https://yihui.org/litedown

Use pkg_citation() to obtain the citation information for the R package. This function requires no arguments.

```r
litedown::pkg_citation()
```

--------------------------------

### Include LaTeX math environments

Source: https://yihui.org/litedown

Use standard LaTeX environments like align or equation for complex mathematical formatting.

```latex
\begin{align}
a^{2}+b^{2} & =  c^{2}\\
\sin^{2}(\theta)+\cos^{2}(\theta) & =  1
\label{eq:pyth-identity}
\end{align}

\begin{equation}
  \begin{split}
  (a+b)^2 &=(a+b)(a+b)\\
    &=a^2+2ab+b^2
  \end{split}
\end{equation}
```

--------------------------------

### Configure graphics device defaults

Source: https://yihui.org/litedown

The dev.args option allows passing a list of arguments to the graphics device function.

```r
list(units = "in", onefile = FALSE, width = 8, height = 8, res = 84)
```

--------------------------------

### R File/Text Output with fuse() and mark()

Source: https://yihui.org/litedown

Demonstrates the default behavior of fuse() and mark() where file input yields file output and text input yields text output.

```r
fuse('foo.Rmd')  # returns a file 'foo.html' or 'foo.tex', etc.
```

```r
mark('Hello _world_')  # returns text
```

```r
mark(text = 'Hello _world_')  # text
```

--------------------------------

### R File Output with Specific Extensions

Source: https://yihui.org/litedown

Illustrates generating file output with specific extensions when the input is a file. The '.pdf' extension triggers conversion to LaTeX and then to PDF.

```r
mark('foo/bar.md', output = '.html')  # file 'foo/bar.html'
```

```r
mark('foo/bar.md', output = '.pdf')   # file 'foo/bar.pdf'
```

--------------------------------

### Demonstrate Verbatim Content Parsing

Source: https://yihui.org/litedown

Shows how litedown handles nested code blocks and inline expressions without parsing them.

```markdown
````md
Below is not a code chunk but verbatim content
inside a fenced code block (with four backticks).

```{r}
1 + 1
```

Inline code expressions like `{r} 1+1` are not
parsed, either.
````
```

--------------------------------

### Get Package Source Code with pkg_code()

Source: https://yihui.org/litedown

Use pkg_code() to retrieve information about the source code of the R package. This function requires no arguments.

```r
litedown::pkg_code()
```

--------------------------------

### Manage Chunk Options

Source: https://yihui.org/litedown

Initializes the mutable environment for managing chunk options.

```R
litedown::reactor()
```

--------------------------------

### Setting Global Options and Restoring

Source: https://yihui.org/litedown

Illustrates setting new global chunk options and then restoring the original values using `litedown::reactor()`. This is crucial when modifying global options outside a document compilation.

```r
# reactor() returns old values after setting new values
old_opts = litedown::reactor(echo = FALSE, fig.height = 6)

# fuse a document with new global chunk options
litedown::fuse("foo.Rmd")

# restore old option values
litedown::reactor(old_opts)
```

--------------------------------

### Customize output formats in _litedown.yml

Source: https://yihui.org/litedown

Define output formats and options for books or websites within the project configuration file.

```yaml
output:
  html:
    options:
      toc:
        depth: 4
  latex:
    meta:
      documentclass: "book"

```

--------------------------------

### Identify normal code blocks

Source: https://yihui.org/litedown

Examples of fenced code blocks that are treated as plain Markdown rather than executable chunks due to syntax variations.

```markdown
```r
# lack of {} in the header
```
```

```markdown
``` {.r, echo = FALSE}
# the language name should not start with "."
```
```

--------------------------------

### Configure External Link Behavior

Source: https://yihui.org/litedown

Enable opening external links in new browser windows.

```yaml
js: ["@external-link"]
```

--------------------------------

### Create a Tip Callout Block

Source: https://yihui.org/litedown

Use a fenced Div with the class `callout-tip` to create a tip-style callout. Arbitrary content, including blockquotes and nested callouts, can be included.

```markdown
::: callout-tip
This is a tip.

> You can write arbitrary content, such as a blockquote.

You can even _nest another callout_ into this one!

Is that cool?
:::
```

--------------------------------

### Activate Initial Tab with 'active' Class

Source: https://yihui.org/litedown

Use the `active` class on a heading to make it the initially displayed tab in a tabset.

```markdown
### Tab two {.active}

Content.
```

--------------------------------

### List xfun::record_print methods

Source: https://yihui.org/litedown

Displays the available S3 methods for the default print function.

```R
methods(xfun::record_print)
```

--------------------------------

### Configure Chapter TOC

Source: https://yihui.org/litedown

Enable the chapter table of contents feature.

```yaml
js: ["@chapter-toc"]
```

--------------------------------

### Include Chart.js Library

Source: https://yihui.org/litedown

Import the Chart.js library using litedown's vest function. This allows for the creation of various chart types.

```r
litedown::vest(js = '@npm/chart.js')
```

--------------------------------

### Define Custom Callout Styling with CSS

Source: https://yihui.org/litedown

Customize the appearance of callouts by defining CSS rules for specific callout classes. This example sets a red background and yellow text for `callout-important`.

```css
.callout-important {
  background: red;
  color: yellow;
}
```

--------------------------------

### Display chunk fences in output

Source: https://yihui.org/litedown

Use N+1 pairs of curly braces in the opening fence to show the chunk fences and options in the rendered output.

```markdown
```{{r}}
#| echo = TRUE, eval = FALSE

1 + 1
```
```

```markdown
```{r}
#| echo = TRUE, eval = FALSE

```
1 + 1
```

--------------------------------

### End a Tabset Explicitly with a Comment

Source: https://yihui.org/litedown

To end a tabset without a higher-level heading, insert a comment in the format `<!--tabset:ID-->`, where `ID` matches the tabset's starting element ID.

```markdown
## Demo tabs {.tabset #foo}

### Tab one

### Tab two

<!--tabset:foo-->

### Not a tab
```

--------------------------------

### Create Leaflet Map with Marker and Circles

Source: https://yihui.org/litedown

Initialize a Leaflet map, set its view, add a tile layer, place a marker with a popup, and draw multiple circles based on provided data.

```javascript
const map = L.map('unmc').setView(`{ loc }`, 17);

// add a tile layer
L.tileLayer('https://tile.openstreetmap.org/{z}/{x}/{y}.png', {
    maxZoom: 21,
    attribution: '&copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a>'
}).addTo(map);

// add a marker and bind a popup to it
const marker = L.marker(`{ loc }`).addTo(map);
marker.bindPopup("<b>UNMC</b><p>You can play badminton here.</p>");

// draw a circle of circles (lat/long from the data frame `circles`)
`{ unname(circles) }`.forEach(row => L.circle(row, {
  color: 'orangered', radius: 30,
  fillColor: 'lightskyblue', fillOpacity: 0.5
}).addTo(map));
```

--------------------------------

### Define book configuration

Source: https://yihui.org/litedown

Specify book-level settings such as input patterns and chapter metadata in the _litedown.yml file.

```yaml
book:
  input: null
  new_session: false
  subdir: false
  pattern: "[.]R?md$"
  chapter_before: "Information before a chapter."
  chapter_after: "This chapter was generated from `$input$`."

```

--------------------------------

### Inspect Graphics Device Defaults

Source: https://yihui.org/litedown

Check the default file naming patterns for common graphics devices.

```r
formals(png)[[1]]
#> [1] "Rplot%03d.png"
formals(svg)[[1]]
#> if (onefile) "Rplots.svg" else "Rplot%03d.svg"
```

--------------------------------

### Configure offline resource directory

Source: https://yihui.org/litedown

Setting a custom directory name for downloaded web resources.

```yaml
offline: "resources"
```

--------------------------------

### Initialize Simple-Datatable from HTML Table

Source: https://yihui.org/litedown

Initialize a simple-datatables instance on an existing HTML table element. Customize pagination with `perPage` and `perPageSelect` options.

```javascript
new simpleDatatables.DataTable('#mtcars > table', {
  perPage: 1,
  perPageSelect: [1, 2, 4, 8, ['All', 0]]
});
```

--------------------------------

### Include external CSS and JS files

Source: https://yihui.org/litedown

Load external assets by defining them in the html output metadata.

```yaml
---
output:
  html:
    meta:
      css: ["one.css", "two.css"]
      js: ["three.js", "four.js"]
---
```

--------------------------------

### Configure Format-Specific Metadata

Source: https://yihui.org/litedown

Specify format-specific metadata variables under `output -> * -> meta`, where `*` can be `html` or `latex`. This includes options like CSS/JS files for HTML and document class/header includes for LaTeX.

```yaml
---
title: "My Title"
output:
  html:
    meta:
      css: "style.css"
      js: "script.js"
  latex:
    meta:
      documentclass: "book"
      header_includes: "\usepackage{microtype}"
---

```

--------------------------------

### Reference local asset files

Source: https://yihui.org/litedown

Load local files by providing the relative path to the repository directory.

```yaml
js: ["repo/path/js/callout.js"]
```

--------------------------------

### Add assets using litedown::vest()

Source: https://yihui.org/litedown

Use the vest function in R Markdown chunks to include assets by feature name or direct file path.

```r
```{r, echo = FALSE}
# add assets by feature
litedown::vest(feature = c('callout', 'copy-button'))
# or add css/js directly
litedown::vest(css = c('@callout', '@book'), js = '@callout')
```
```

--------------------------------

### Configure YAML output fields

Source: https://yihui.org/litedown

Specify additional fields like latex_engine or templates under the output format in YAML.

```yaml
output:
  latex:
    latex_engine: xelatex
    keep_md: true
    template: custom-template.tex
```

--------------------------------

### Include Simple-datatables Assets

Source: https://yihui.org/litedown

Add the necessary CSS and JavaScript files for the simple-datatables library. This is a prerequisite for using its features.

```r
litedown::vest(css = '@npm/simple-datatables/dist/style', js = '@npm/simple-datatables')
```

--------------------------------

### Configure HTML Options in YAML

Source: https://yihui.org/litedown

Set various HTML output options, such as enabling a table of contents and configuring JavaScript syntax highlighting, using YAML.

```yaml
output:
  html:
    options:
      toc: true
      js_highlight:
        package: highlight
        theme: github
        languages: [diff, latex]
```

--------------------------------

### Control text output behavior

Source: https://yihui.org/litedown

Demonstrates the results option to show, hide, or render text output as Markdown.

```R
```{r, test-out}
cat('Hello _world_!\n')
```
```

```R
```{r, test-out, results = FALSE}
```
```

```R
```{r, test-out, results = 'asis'}
```
```

--------------------------------

### Automatic Heading IDs

Source: https://yihui.org/litedown

Demonstrates how headings are converted to HTML with automatic IDs. Prefixes like `chp:` and `sec:` are added based on heading level. IDs can be manually overridden.

```markdown
# Hello world!

## Introduction

```

```html
<h1 id="chp:hello-world">Hello world!</h1>

<h2 id="sec:introduction">Introduction</h2>

```

```markdown
# Hello world! {#hello}

```

--------------------------------

### Use the Markdown engine

Source: https://yihui.org/litedown

The md engine outputs Markdown text verbatim and as-is.

```markdown
```{md}
You can see both the _source_ and _output_ of
this `md` chunk.
```

You can also use `{md} the engine **inline**`.
```

--------------------------------

### Include Callout CSS and JavaScript

Source: https://yihui.org/litedown

To use callout blocks, include the `callout.css` and `callout.js` files in your document's configuration.

```yaml
css: ["@callout"]
js: ["@callout"]
```

--------------------------------

### Looping in R

Source: https://yihui.org/litedown

A standard for loop structure in R.

```r
for (i in 1:10) {
}
```

--------------------------------

### Add litedown to Suggests

Source: https://yihui.org/litedown

If litedown is not a hard dependency, add 'Suggests: litedown' to your package's DESCRIPTION file.

```r
Suggests: litedown

```

--------------------------------

### List litedown Markdown Options

Source: https://yihui.org/litedown

This code snippet lists all available litedown markdown options, showing which are enabled or disabled.

```r
litedown::markdown_options()
#>  [1] "-cleveref"         "-hardbreaks"       "-number_sections" 
#>  [4] "-offline"          "-smartypants"      "-tagfilter"       
#>  [7] "-toc"              "+auto_identifiers" "+autolink"        
#> [10] "+cross_refs"       "+embed_cleanup"    "+embed_resources" 
#> [13] "+footnotes"        "+js_highlight"     "+js_math"         
#> [16] "+latex_math"       "+smart"            "+strikethrough"   
#> [19] "+subscript"        "+superscript"      "+table"           
#> [22] "+tasklist"        

```

--------------------------------

### YAML Metadata for Markdown Options

Source: https://yihui.org/litedown

Configure Markdown rendering options like math package, section numbering, and resource embedding via YAML metadata. This is the recommended approach for setting options.

```yaml
---
output:
  html:
    options:
      js_math:
        package: "katex"
        version: "0.16.4"
      number_sections: true
      embed_resources: ["local", "https"]
    meta:
      css: "custom.css"
---
```

--------------------------------

### Create a Tabset with an Empty Div

Source: https://yihui.org/litedown

Define a tabset by using an empty fenced Div with the class name `tabset`. Subsequent headings will become tabs.

```markdown
:::
::: tabset
:::

## Tab one

Content.

## Tab two

Content.
```

--------------------------------

### Configure Paged HTML

Source: https://yihui.org/litedown

Enable paged layout support for HTML documents.

```yaml
css: ["@pages"]
js: ["@pages"]
```

--------------------------------

### Enable Code Folding with JavaScript

Source: https://yihui.org/litedown

Include the `@fold-details` JavaScript file to enable code folding functionality for elements.

```yaml
js: ["@fold-details"]
```

--------------------------------

### Include external CSS and JS

Source: https://yihui.org/litedown

Use href or src chunk options to link external stylesheets or scripts.

```css
```{css, href="https://unpkg.com/mvp.css"}
```
```

```javascript
```{js, src="https://cdn.jsdelivr.net/npm/@xiee/utils/js/math-code.js"}
```
```

--------------------------------

### Configure TOC Highlighting

Source: https://yihui.org/litedown

Enable highlighting for items in the table of contents.

```yaml
js: ["@toc-highlight"]
```

--------------------------------

### Insert CSS and JS

Source: https://yihui.org/litedown

Use css and js engines to inject styles and scripts into the output.

```css
```{css}
a {
  color: red;
}
```
```

```javascript
```{js}
document.body.classList.add('dark');
```
```

--------------------------------

### Collapse source and output blocks

Source: https://yihui.org/litedown

Use collapse = TRUE to merge adjacent source code and verbatim text output blocks for a more compact appearance.

```r
```{r, collapse = TRUE}
x = 1:5
x
#> [1] 1 2 3 4 5
x + 100
#> [1] 101 102 103 104 105
```
```

--------------------------------

### Initialize Simple-Datatable with JSON Data

Source: https://yihui.org/litedown

Render a data table using simple-datatables by providing data as a JSON object. Configure options like headings and data rows.

```javascript
new simpleDatatables.DataTable('#table-iris', {
  data: {
    headings: `{ names(iris) }`,
    data: `{ unname(iris)[1:20, ] }`
  },
  perPage: 5
});
```

--------------------------------

### Configure Centered Images

Source: https://yihui.org/litedown

Enable automatic centering for images.

```yaml
js: ["@center-img"]
```

--------------------------------

### Create a Tabset with a Specific ID

Source: https://yihui.org/litedown

Initiate a tabset with a specific ID using a fenced Div. Subsequent headings will be converted to tabs.

```markdown
::: {.tabset #foo}
:::

## Tab one

## Tab two

<!--tabset:foo-->

## Not a tab
```

--------------------------------

### Plot File Configuration Options

Source: https://yihui.org/litedown

Options used to customize the generation, sizing, and pathing of plot files.

```APIDOC
## Plot File Configuration Options

### Description
These options manage the technical aspects of plot file generation, such as file extensions, dimensions, and storage paths.

### Parameters
- **fig.ext** (string) - Optional - The plot file extension (e.g., .png, .svg).
- **fig.height** (numeric) - Optional - Physical height of the plot in inches.
- **fig.width** (numeric) - Optional - Physical width of the plot in inches.
- **fig.dim** (vector) - Optional - Shorthand for setting both width and height as c(width, height).
- **fig.keep** (numeric/logical/string) - Optional - Indices of plots to keep; can be numeric, logical, or 'last'.
- **fig.path** (string) - Optional - Path prefix for generated plot files.
```
Tokens:
Raw