function combineTagValues(value, newValue) {
    if (value === undefined) return newValue
    if (value instanceof Array) {
      value.push(newValue)
      return value
    }
    return [value, newValue]
  }
Combines IPTC value with existing ones.

@param {object} value Existing IPTC field value
@param {object} newValue New IPTC field value
@returns {object} Resulting IPTC field value