[ODE] Joints, ERP and CFM

[Dimitris Papavasileiou]

Hi,
I'm new to ode (I haven't written any ode-related code yet) but I've read
through all the docs I could find trying to understand how it works and how
to integrate it in my own project. Could someone clarify the following
points regarding joints to me:

1) How come there is a dParamCFM parameter for joints but not a dParamERP
parameter (erp seems to be available only for constacts, stops and suspensions)?
2) Also how do these global ERP and CFM parameters (and all global
parameters like autoenable) work? When is the global value used and when the
local value?
3) How would it be for example possible to create two bodies connected by a
"spring loaded slider joint", that is, the bodies should move on the same
axis (the slider axis) as though connected by a spring. Do I use a slider
joint with both high and low stops at 0 and suitable cfm and erp values for
the stops according to the formulas in the manual?

Thanks in advance,
Dimitris