Get Value Information using EL Expressions

Summary:

I'm looking for a way to get information using EL Expression that are stored in a Custom Field.

Is there any documentation or guide reference regarding on how to use EL Expressions as a URL parameter in Structure?

Content (required):

Hi,

I'm currently trying to pass a parameter value from the destination URL from Structure, using EL Expressions.

The value that I'm trying to extract is from a custom field that will become the parameter value for the URL.

But for now, I don't have enough documentation provided regarding this topic, so I'm hoping if there's any guidance or documentation reference for this.