# Expression binding in template

**URL:** <https://forum.inductiveautomation.com/t/expression-binding-in-template/116705>\
**Category:** Ignition\
**Created:** [August 7, 2026, 5:39pm UTC](https://forum.inductiveautomation.com/t/expression-binding-in-template/116705 "2026-08-07T17:39:40Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![oscar.villarreal](https://avatars.discourse-cdn.com/v4/letter/o/b9e5f3/32.png) [@oscar.villarreal](https://forum.inductiveautomation.com/u/oscar.villarreal)\
**Post date:** [August 7, 2026, 5:39pm UTC](https://forum.inductiveautomation.com/t/expression-binding-in-template/116705/1 "2026-08-07T17:39:40Z")

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Hello,

I am creating a template and trying to bind a template parameter and keep getting this error. I am new to scripting and would appreciate assistance.

 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/a/a/aa85e81c2531739336145cbf27545bbb598d030e.png)

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<div class="post-metadata">

**Author:** ![lrose](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/lrose/32/62724_2.png) [@lrose](https://forum.inductiveautomation.com/u/lrose)\
**Post date:** [August 7, 2026, 5:46pm UTC](https://forum.inductiveautomation.com/t/expression-binding-in-template/116705/2 "2026-08-07T17:46:14Z")

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You can not nest a tag path into another tag path. Which is exactly what the error message is telling you.

This syntax:

```python
{[WinProcessing]ALSAFE_{Alsafe.TANK_NUM}/valve/V107B.value}

```

Is illegal in the expression language.

What you should do insead is create a custom property which you bind with an IndirectTag Binding for each of the paths. Then this epression would look something like:

```python
{Alsafe.V107B} || {Alsafe.V107A}

```

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<div class="post-metadata">

**Author:** ![oscar.villarreal](https://avatars.discourse-cdn.com/v4/letter/o/b9e5f3/32.png) [@oscar.villarreal](https://forum.inductiveautomation.com/u/oscar.villarreal)\
**Post date:** [August 7, 2026, 8:15pm UTC](https://forum.inductiveautomation.com/t/expression-binding-in-template/116705/3 "2026-08-07T20:15:17Z")

</div>

Do I do this on the template?

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<div class="post-metadata">

**Author:** ![lrose](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/lrose/32/62724_2.png) [@lrose](https://forum.inductiveautomation.com/u/lrose)\
**Post date:** [August 7, 2026, 8:51pm UTC](https://forum.inductiveautomation.com/t/expression-binding-in-template/116705/4 "2026-08-07T20:51:15Z")

</div>

Yes

Best practice for templates particularly for UDTs is to pass the tag path to the least descriptive part, for instance the parent folder/UDT and use custom properties and indirect bindings to grab all of the needed values for that template.

Do NOT use UDT parameters.