what is the difference between {{}} and [[]] in the the template data binding?

[wilby yang]

I sometimes come across {{}} syntax and sometimes [[]] in the template data binding. I am rather sure [[]] usage, which is referring the properties in the component. but what does {{}} do?

[Jan Meijering]

The curly brackets is representing two way binding, the square ones one way:

https://www.polymer-project.org/1.0/docs/devguide/data-system#data-flow-control