How does CUPS scheduler decide next filter / backend?

[anonymous]

When CUPS scheduler calculates cost of filters, how does it know what file 
format (PCL/PS) backend is expecting?

Basically I want to print PCL files to my PCL printer, but I don't want to 
create a special raw queue for that. (It doesn't make sense, ps, text, 
image, pdf all send to the same queue, why pcl file need to sent to a 
special queue?)

I want to create a filter, and added an entry in *cupsFilter in the PPD 
file. How can CUPS know my pcl2pcl filter is the last filter?

Another question is when pipe a couple of filters together, how could a 
filter know which / whether the user option has been processed?
I want to have my own myps2ps filter and support my own user option like 
"duplex=simplex". Do I need to remove that option from option list before 
passing it down to pstops ?

When foomatic-rip get vnd.cups-postscript, does it add PJL/postscript to the 
file again?

Thanks