# References

The **CommsDSL** allows references to fields or other definitions in order not to duplicate information and avoid various copy/paste errors. The referenced element **must** be defined (if in the same file) or processed (if in [different](/commsdsl-specification/multiple_files.md) schema file) **before** the definition of the referencing element.

For example, message defines its payload as a reference (alias) to the globally defined field. This field is defined before the message definition. the opposite order **must** cause an error. It allows easy avoidance of circular references.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <fields>
        <int name="SomeField" type="uint8" />
    </fields>

    <message name="SomeMessage" id="1">
        <ref field="SomeField" />
    </message>
</schema>
```

When referencing a field or a value defined in a namespace (any namespace, not just different one), the former must be prefixed with a namespace(s) name(s) separated by a **.** (dot).

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <ns name="myns">
        <fields>
            <int name="SomeField" type="uint8" />
        </fields>

        <ns name="subns">
            <fields>
                <int name="SomeOtherField" type="uint16" />
            </fields>
        </ns>

        <message name="SomeMessage" id="1">
            <ref field="myns.SomeField" />
            <ref field="myns.subns.SomeOtherField" />
        </message>
    </ns>
</schema>
```


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