code: func (s StringSlice) IndexOfIgnoreCase(str string) int {
  	str = strings.ToLower(str)
  	for i, v := range s {
  		if str == strings.ToLower(v) {
  			return i
  		}
  	}
  
  	return -1
  }
docs: // IndexOfIgnoreCase looks for specified string, disregarding letter casing,
  // into current slice.