How to express "or" in EC Expression?

Hi, Everyone

I have a question about how to express "or" in EC expression.

I know ‘|’ represents "or" in EC Expression, but still haven't found a right way to achieve what I need.

I am writing the Name expression of equipment. What I want to accomplish is: if the content in 'C_UNIT_SUFFIX' is "<None>" or "NA". Then, we don't need 'C_UNIT_SUFFIX' show in the Name of Equipment.

Following is the EC Expression I write in schema now, anyone has idea where should I add '|' to achieve my aim?

this.C_DEPARTMENT_CODE & this.UNIT & IIF(this.C_UNIT_SUFFIX= "<None>","",this.C_UNIT_SUFFIX) & this.DEVICE_TYPE_CODE & IIF(System.String.Length(this.NUMBER)<= 0 ,"?" ,System.String.Format("{0:D3}",(this.NUMBER)*1))