PNF (proprioceptive muscular facilitation) is entirely different.
The following site has a good explanation of the principles involved: http://www.thestretchinghandbook.com...stretching.php
Please note the warning that injury can be incurred.
In fact, exactly what really is happening at the cellular level is open for debate.
Since muscle is much easier to tear than "scar tissue", does the increase in range of motion really result from multiple small muscle tears?
Another question: How many who try this technique actually experience a hamstring or other muscle tear?
But if you are interested here are some other sites with fairly understandable language (many sites are heavy into muscle physiology terminology):
Sports Fitness Advisor http://www.sport-fitness-advisor.com/pnfstretching.html