# Expression for UDT Instance Documentation from Subfolders

**URL:** <https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755>\
**Category:** Ignition\
**Tags:** ignition81\
**Created:** [March 29, 2022, 12:50pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755 "2022-03-29T12:50:36Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![deon.korb](https://avatars.discourse-cdn.com/v4/letter/d/8c91f0/32.png) [@deon.korb](https://forum.inductiveautomation.com/u/deon.korb)\
**Post date:** [March 29, 2022, 12:50pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/1 "2022-03-29T12:50:37Z")

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I’m trying to reference the documentation of a UDT instance (`UDTInstance.Documentation`) in a UDT tag expression (ultimately in an alarm label binding)

Getting the documentation from a flat structure is easy using `[.].Documentation`  
 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/d/adc9f38389efe750a96c6eca6236b7293699934f.png)

How do you get it using a relative reference if there are folders involved?  
 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/9/d907581c9481a1d5584623c18df18b3f5958a047.png)

I’ve tried the following without success:

```auto
[.]../../.Documentation
[.]../...Documentation

```

The [documentation](https://docs.inductiveautomation.com/display/DOC81/Tag+Paths#TagPaths-UsingRelativeTagPaths) on this doesn’t seem to cover this use case, or I’m not seeing it.

What is the correct relative reference for this?

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<div class="post-metadata">

**Author:** ![cconnor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/cconnor/32/33235_2.png) [@cconnor](https://forum.inductiveautomation.com/u/cconnor)\
**Post date:** [March 29, 2022, 7:11pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/2 "2022-03-29T19:11:47Z")

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To reference the Documentation of the ‘DocTopLevel’ tag in the Expression of the ‘DocDeep’ tag, try setting the Expression to ‘{[.]…/…/DocTopLevel.Documentation}’.

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<div class="post-metadata">

**Author:** ![deon.korb](https://avatars.discourse-cdn.com/v4/letter/d/8c91f0/32.png) [@deon.korb](https://forum.inductiveautomation.com/u/deon.korb)\
**Post date:** [March 29, 2022, 7:17pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/3 "2022-03-29T19:17:45Z")

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I’m trying to reference the documentation of the UDT instance, not of the child member.

I.e. TestDocs.Documentation

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<div class="post-metadata">

**Author:** ![cconnor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/cconnor/32/33235_2.png) [@cconnor](https://forum.inductiveautomation.com/u/cconnor)\
**Post date:** [March 29, 2022, 10:45pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/4 "2022-03-29T22:45:54Z")

</div>

Understood, I am able reference the Documentation of the UDT Instance by specifying the tag path to the UDT instance in the Expression. For instance: ‘{[~]TestDocs.Documentation}’.

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<div class="post-metadata">

**Author:** ![deon.korb](https://avatars.discourse-cdn.com/v4/letter/d/8c91f0/32.png) [@deon.korb](https://forum.inductiveautomation.com/u/deon.korb)\
**Post date:** [March 30, 2022, 6:50am UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/5 "2022-03-30T06:50:43Z")

</div>

This is not a solution as it refers to the UDT instance name and relies on the fact that the UDT instance is in the root of the tag provider.

What I require is an relative refers in the UDT definition, 2 folders deep that references the UDT instance documentation, regardless of what the where the UDT is instantiated or what it is called.

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<div class="post-metadata">

**Author:** ![cconnor](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/cconnor/32/33235_2.png) [@cconnor](https://forum.inductiveautomation.com/u/cconnor)\
**Post date:** [March 31, 2022, 7:01pm UTC](https://forum.inductiveautomation.com/t/expression-for-udt-instance-documentation-from-subfolders/57755/6 "2022-03-31T19:01:24Z")

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I have not found a way to get this to work using relative tag path syntax. However, you can try building a dynamic tag path to the Documentation property of the UDT instance and using the ‘tag’ Expression function to read the value of the property. For example: 'tag(concat({ParentInstanceName}, “.Documentation”)).