Composing validation rules in another list and user input

Hi

I am using Nintex 2019. I have a requirement for validation on a single line text field that I am hoping would be detailed in the pseudo code below. The code is activated

1. Load existing values from a column in another list.
2. Split the values to identify the required text (ABC123 <User input>) - ABC123 is the required text.
3. Split the values in the single text field, with the similar text entry as in (2). Match specifically the required text.
4. If this exists / matches, display an error message.

The functionality I can think of that is required is to

• store values in a variable to be retrieved.
• RegEx to match the required text.
• Split the text input into components - similar to Regex
• Debugging - console.log?

I was thinking of writing this, NOT using JavaScript but in validation syntax. I would appreciate any advice in this too. I will be implementing this in the ‘Save’ button in the “Causes validation - Expression’.

What I was thinking of is something like this -

List-Name “The List” (and this is where I am stuck)

Would appreciate any pointers.

lielar