---
title: md-values - Mission Director values
summary: MD uses expressions, object references, lists, tables and unit-bearing values. An XSD attribute type does not declare the type of event.param. Actions can write variables rather than return Lua values.
section: reference
kind: guide
status: reference
updated: 2026-10-26
tags: ["API","X4"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/","https://www.lua.org/manual/5.1/manual.html","https://luajit.org/ext_ffi_api.html"]
---
## Meaning

MD uses expressions, object references, lists, tables and unit-bearing values. An XSD attribute type does not declare the type of event.param. Actions can write variables rather than return Lua values.

## Example

```xml
<set_value name="$Amount" exact="12" />
```

**What happens:** The MD variable $Amount becomes the number 12.

This fragment does not print or write a log message. The values shown are the expected results of the example.

## Methods and related calls

[API reference](wiki:api-index).