code: func (c *Characteristic) AddDescriptor(d *Descriptor) *Descriptor {
  	for _, x := range c.Descriptors {
  		if x.UUID.Equal(d.UUID) {
  			panic("service already contains a characteristic with UUID " + d.UUID.String())
  		}
  	}
  	c.Descriptors = append(c.Descriptors, d)
  	return d
  }
docs: // AddDescriptor adds a descriptor to a characteristic.
  // AddDescriptor panics if the characteristic already contains another descriptor with the same UUID.