Need some help understanding the solution in chapter 14 (F3 Discovery book)

[avsaase]

In the solution given in 14.4 the following code is use to send the START signal to the I2C device:

i2c1.cr2.write(|w| {
    w.start().set_bit();
    w.sadd().bits(MAGNETOMETER);
    w.rd_wrn().clear_bit();
    w.nbytes().bits(1);
    w.autoend().clear_bit()
});

(I have the board with the LSM303AGR but this part of the code is identical).

It looks like this corresponds to what the LSM303AGR datasheet in 6.1.1 I2C operation says:

The transaction on the bus is started through a start (ST) signal. A start condition is defined
as a high to low transition on the data line while the SCL line is held high. After this has been
transmitted by the master, the bus is considered busy. The next byte of data transmitted
after the start condition contains the address of the slave in the first 7 bits and the eighth bit
tells whether the master is receiving data from the slave or transmitting data to the slave.

Can someone explain what each line of this code does exactly or where I can find this information? I would like to better understand how this code works so I can write code to interface with other peripherals.