I was reading up on the new 'svn cp --pin-externals' feature in the 1.9 release notes. Great addition, by the way, and one that I hope to use myself with ViewVC's release tags.
One question came to mind, though. The use of the feature appears to result in pegged externals definitions (as in, @-bearing URLs). That's great and obviously the correct approach. But if I recall correctly, this means that use of the feature will cause the copy's externals to be written in a way that older (pre-1.5) clients do not understand. Is that correct? If so, I think that's a fine limitation to have -- no complaints at all here. But perhaps this merits a mention in the Compatibility section of the release notes? -- Mike