There are a lot docunment in User manul of Spoon. But these only work for the fields which input from file or database or export from previous steps.

But these still a lot fuction which apply to variable claimed in javascript, and for use in the variable in current script, for example,
for fields, we use subStr() while to local variable, we have to use substring(), so where can I find these functions?

And also, these're a lot internal system level functions as, how can I find them? Are there document available?

Thanks a lot.