Thanks for this simple but very clear explanation Julia! I tried to look into it a few weeks ago and found the website and other articles to be somewhat too abstract for me to understand quite what it was. A lot of what I found talked about it as if the reader already knew these more basic points you just spelled out. Maybe there's more of this type of explanation out there now ,I haven't looked in a while . But I just signed up because I now see why I would want to! Thanks!