[The Geek]

hybrid - changed in 4.0

venom - this has changed in 4.0 as I think it was (and is) confusing to people.
Essentially if you had replacement code in the settings - you didnt ever have to put replacement code in any categories or individual items - it is a 'global' value. However you could 'override' the global by putting replacements in at the category level.
THe idea being that the global would be the default - but then you could have category override it.
FInally - you could also put replacement code at the individual item level which would override the category setting.

Anyway - as handy as it is - I think its confusing and overkill. In 4.0 Most settings are handled at the category level