[Click] a question about how to write elements

[刘晓佳]

Hello,

I am new to click.I want to write my own elements.But I am puzzle over the
mechannism of click,and have some questions, hope someone could give me
help.
1、which function calls push function and other functions, such as cast
function?
2、where can a function receive an actual parameter ?For example ,cast
function and push function.

Regards,

Xiaojia Liu