---
title: set_value
summary: MD assignment and counter increment forms observed in this project.
section: reference
kind: api
status: reference
tags: ["X4","modding","set","value"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/"]
---
## Return value

| Type | Meaning |
| --- | --- |
| [none (MD action)](wiki:type-md-values) | Writes an MD variable; its value type depends on the expression and attributes. |

[Types and methods](wiki:types)

## Assignment


Layer: Mission Director actions. `name` is the variable path, `exact` is the value expression and `operation`, when present, selects how to apply it. Examples initialize a string, number and table.




```xml
<set_value name="$Label" exact="'example'" />
<set_value name="$Revision" exact="0" />
<set_value name="$Records" exact="table[]" />
```



**What happens:** In the current MD context, $Label = "example", $Revision = 0 and $Records is an empty MD table. Nothing is logged.

## Increment a revision


The counter must already exist with the appropriate type. Initialization and migration of saved state require their own design.




```xml
<set_value name="$Revision" operation="add" exact="1" />
```



**What happens:** If $Revision is 0 after initialization, it becomes 1; this changes the variable in the stated context.

## Scope


`$Revision` in the current context and `Init.$Revision` are not necessarily the same variable. For instantiated handlers, distinguish request-local data from a shared registry. This is not the full attribute reference; check the XSD and game behavior for new forms. See [MD variables](wiki:md-variables) and [migrations](wiki:md-persistence).