Svn:Externals as compared to "sharing"

There is consensus here that our next SCM should have the "sharing"
feature. I'm curious about the externals property, how it compares to
sharing, and how it might be better or worse than sharing. For example,
can one update an externally referenced project seamlessly (in our case,
we're evaluating Ankh in VS 2005 and TortoiseSVN)?

If so, will the workspace recognize a change in the svn:external
definition in the repository on update or commit and halt the operation
until the user handles the change? I read the section in the book and
it looks like it will do some of these things, to a point. The need to
update the external workspaces separately is odd, for example, but I
think I understand the technical reason for it.

If there's any Ankh/Tortoise experts here, I'm curious if they recognize
embedded externals. Can Ankh handle multiple SVN projects in the same
solution seamlessly? I know there are separate lists for these products
- I'm just curious if anybody here already knows.

--
David
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