# set_header: Set the header information In knitr: A General-Purpose Package for Dynamic Report Generation in R

### Description

Some output documents may need appropriate header information. For example, for LaTeX output, we need to write \usepackage{tikz} into the preamble if we use tikz graphics; this function sets the header information to be written into the output.

### Usage

```set_header(...)
```

### Arguments

 `...` Header components; currently possible components are `highlight`, `tikz` and `framed`, which contain the necessary commands to be used in the HTML header or LaTeX preamble. Note that HTML output does not use the `tikz` and `framed` components, since they do not make sense in the context of HTML.

### Details

By default, knitr will set up the header automatically. For example, if the tikz device is used, knitr will add \usepackage{tikz} to the LaTeX preamble, and this is done by setting the header component `tikz` to be a character string: ```set_header(tikz = '\usepackage{tikz}')```. Similary, when we highlight R code using the highlight package (i.e. the chunk option `highlight = TRUE`), knitr will set the `highlight` component of the header vector automatically; if the output type is HTML, this component will be different – instead of LaTeX commands, it contains CSS definitions.

For power users, all the components can be modified to adapt to a customized type of output. For instance, we can change `highlight` to LaTeX definitions of the listings package (and modify the output hooks accordingly), so we can decorate R code using the listings package.

### Value

The header vector in `opts_knit` is set.

### Examples

```set_header(tikz = "\\usepackage{tikz}")