# Substitutions

Substitutions are variables. They are declared in any document and defined in the `conf.py` file, `rst_prolog` setting.

## Default substitutions

Projects using the theme can use the following substitutions:

* `|v|` for <i class="inline-icon icon-check" aria-hidden="true"></i>
* `|x|` for <i class="inline-icon icon-cancel" aria-hidden="true"></i>

## Substitutions within code blocks

To add substitutions within [Code blocks](https://sphinx-theme.scylladb.com/branch-1.8/examples/code-blocks.md), pass the option `:substitutions:` to the `code-block` directive.

For example:

```rst
.. code-block::
  :substitutions:

  |rst|
```

Renders as:

```default
restructuredText
```