zk/docs/config-extra.md

# Extra user variables

`zk` is opened for template context extension which can be useful when [creating new notes](note-creation.md), for example:

* expanding custom metadata (author, subject, etc.)
* modifying a [template](template.md)'s output dynamically depending on the value of an extra variable

## Static extra variables

You can declare static extra variables in the [configuration file](config.md)'s `[extra]` section. Each [note group](config-group.md) can have its own `[extra]` section, which may override values from the root section.

```toml
[extra]
visibility = "public"
author = "Mickaël"

[group.journal.extra]
visibility = "private" # overrides
```

## Dynamic extra variables

Maybe more useful, you can provide additional extra variables dynamically to `zk new` from the command-line with `--extra`. Multiple variables can be separated by a comma `,`.

```sh
$ zk new --extra author=Thomas
$ zk new --extra show-header=1,author=Thomas
```

## Using extra variables in templates

After declaring extra variables, you can expand them inside the [template used when creating new notes](template-creation.md), using the usual [Handlebars syntax](template.md).

```markdown
# {{title}}

Written by {{extra.author}}.

{{#if extra.show-header}}
Behold, the mighty dynamic header!
{{/if}}
```