get variable() {
        return this._inner.variable;
    }
@name helpers.Column#variable
@type string
@readonly
@description
Full-syntax formatting variable, ready for direct use in query templates.

@example

const cs = new ColumnSet([
    'id',
    'coordinate:json',
    {
        name: 'places',
        mod: ':csv',
        cast: 'int[]'
    }
]);

// cs.columns[0].variable = ${id}
// cs.columns[1].variable = ${coordinate:json}
// cs.columns[2].variable = ${places:csv}::int[]