Series and Shunt diode Clipper Circuits

do you observed total circuit clearly see the operation of diode and other components so you understand why it occur like that

yes i observed circuit clearly,read different books but couldn't found a clear cut answer to my doubt.i observed that in a zener diode voltage regulator circuit,voltage at output remain constant since zener diode works in reverse biased form and it has a property to maintain a constant voltage across it in the expense of variation in current across it.but what happen to this property when it is placed in series in circuit.why it allows almost all the waveform to pass through it.i think there is not a very big concept behind this as it is not mentioned in books,may be a gap in my basic knowledge about circuits but please help me friends.