Personality Variable

Can anyone tell me what a personality variable is, or how I would declare it?

Here is the code:

if (count(Further_Category_Options[Sub_Categories_Selection == input.Material_Sub_Categories])  ==  0)
{
    clear Further_Category_Options;
}
else
{
    for each subcategory in Further_Category_Options  [Sub_Categories_Selection == input.Material_Sub_Categories.toString]
    {
        Futher_Category_Option_Field:ui.add(subcategory.Futher_Category_Option_Field);
    }
}

In line 7 I added "toString" because otherwise I had this error:

Error in statement at line number 7
The Left expression is of type STRING and the right expression is of type STRINGLIST And the operator == is not valid here

I was hoping to convert the stringlist to a string and make my code work.

Any suggestions?

Thanks!