---
title: relationlookup - X4 schema type
summary: relationlookup: X4 attribute schema type: base types, constraints and value alternatives.
section: reference
kind: guide
status: reference
updated: 2026-10-27
tags: ["XSD","schema","types"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/","https://www.w3.org/TR/xmlschema11-2/"]
---
## Meaning

relationlookup: X4 attribute schema type: base types, constraints and value alternatives.

An XSD type constrains XML, rather than declaring a Lua return or the payload type of event.param. A valid schema value does not prove a successful game effect.

## Schema structure

`libraries/common.xsd`

| Property | Value |
| --- | --- |
| Construction | `restriction` |
| Base type | [`xs:string`](wiki:schema-xs-string-d5652e9b) |

| Constraint | Value |
| --- | --- |
| `enumeration` | `self` |
| `enumeration` | `ally` |
| `enumeration` | `member` |
| `enumeration` | `friend` |
| `enumeration` | `dock` |
| `enumeration` | `neutral` |
| `enumeration` | `enemy` |
| `enumeration` | `killmilitary` |
| `enumeration` | `kill` |
| `enumeration` | `nemesis` |

restriction narrows a base type; union accepts one of its branches; list describes whitespace-separated items. Enumeration values in one restriction are alternatives. Pattern syntax is XML Schema regex, not Lua patterns or JavaScript RegExp. Constraints inherited from the base type still apply.

## Example and result

Use the attribute pages below for contextual examples. A generic executable example is not inferred from a type name alone.

## Used by

| Element | Attribute | Schema |
| --- | --- | --- |
| [`match_relation_to`](wiki:api-md-match-relation-to-f726da41) | `relation` | `libraries/common.xsd` |


[All schema types](wiki:schema-types) · [Lua / MD value types](wiki:types)