Question

Couldn’t find any documentation on this on the Knockout site, other than the knockout mapping plug in exposes it.

Answer 1

sigh – as soon as you post it – you find the answer. Ironically via the knockout site : http://knockoutjs.com/documentation/observableArrays.html
and
http://knockoutjs.com/documentation/plugins-mapping.html

They are functionally equivalent to the regular ko.observableArray
functions, but can do things based on the key of the object.

So in brief:

mappedRemove and mappedRemoveAll removes an element in the same way that remove does, but allows you to do operations on the key.

mappedDestroy and mappedDestroyAll is there as a convenience for Ruby developers and adds _destroy to the object. No idea why – I’m not a Ruby developer.