I have several questions about the filter function

[xzer]

I'm an author of an extension which apply the filters to the outgoing
messages automatically, since the Thunderbird3 beta4 has been
released, so I received many requests for upgrade my extension to be
compatible with the new version, then I did it today.

After I read the source, I have several questions to ask,

1) There is a new option of a filter, "apply filter when"(On source
level, it is the nsMsgFilterTypeType), but it puzzled me, what does
the "after classification" mean? If I checked the option which is not
as "after classification", for example, the first option "Checking",
does it mean that after this filter run, the bays junk judgment will
not be applied (I read the source, it seems like that, but I am not
sure, I need read more...)? In my opinion, these options are too
complex to a user. So I want to know what is the purpose of this
option? Does it really necessary?

2) I noticed that by the nsMsgFilterTypeType define, in fact it become
easily to implement a outgoing filter mechanism, but there is not yet,
and also that I found there is a define of custom javascript type of a
filter and a custom action define, but I didn't see the user interface
of this function, does it just for extension? I want to do some work
about the filter function, but I don't think it's a good idea to do
with an extension, I think the best way is to add the implements to
the core source, so I want to know whether there is a plan of filter
function which is from the Thunderbird development team, I don't want
to do reduplicate work with the development team.