As I understand it, tangzhong in relation to bread making is an Asian technique in which a portion of the flour in the recipe is pre-cooked with water to make a roux, before being cooled and added to the rest of the ingredients. It is supposed to make the resulting bread very soft, often for days longer than non-tangzhong breads. I thought maybe it works by binding the proteins so gluten development is restricted, but I'd have thought that would inhibit rise, which seems not to be an issue.
Disclaimer: I have not yet made a tangzhong bread, but I believe I have eaten a few... My first attempt is currently doing a bulk rise.
How does tangzhong work exactly? How does it actually change the dough to achieve the distinct softness for which it is so famous?