When does the Arduino Wire library actually transmit on the I2C bus ?

I wanted to better understand the inner workings of the Wire library (the I²C library that comes with Arduino IDE).  The detailed reference and source code were helpful.  To check my understanding, I made a simple oscilloscope experiment, which I would like to report in this post.

Setup

Straightforward test code, which creates a write transaction on the I²C bus.  To know when the calls to the Wire library methods happen, each one is preceded by a strobe on pin 13.  These strobes will be seen with an oscilloscope.   To know when the I²C activity actually occurs, SDA and SCL (the I²C data and clock lines) are too observed with the oscilloscope.

  void strobe() {

    digitalWrite(13, HIGH);           // Strobe for oscilloscope
    digitalWrite(13, LOW);

  }

  void loop() {

    strobe();
    Wire.beginTransmission(0x4C);     // Set the address of the target device  

                                      // which we want to write to

    strobe();
    Wire.write(0x07);                 // Payload: set the address of the register inside

                                      // of the external device, which we want to write to

    strobe();
    Wire.write(0x01);                 // Payload: value to write to the register

    strobe();
    Wire.endTransmission();           // Actually do the transmission.

    delay(1000);
  }

This code ran on Arduino LilyPad USB (my clone thereof).  It should work the same on any Arduino that's based on AVR and has got hardware I²C.

(The addressee of this I²C transaction is an MMA7660 accelerometer.  It could have been just about any I²C slave device.)

Results and discussion

As you can see, all of the I²C activity happens after all the calls to the Wire library methods have been made.
Wire.beginTransmission(...) doesn't actually begin the transmission, it only sets the I²C slave address for the forthcoming transmission.
Wire.write(...) doesn't actually transmit, it writes to a buffer in the Arduino's RAM.
Wire.endTransmission() actually causes the whole I²C transaction to happen from beginning to end.

Perhaps, the Wire Library functions could have names that better reflects inner workings.

References

[1]  Wire Library superficial reference
[2]  Wire Library detailed reference
[3]  Source code for Wire Library on GitHub