[notJim]

I'm relatively comfortable with this stuff, but I am confused by your response.

First you say that engines will "internally" replace non-BMP glyphs with the replacement character, but then you give an example that seems to work fine (and I think would work fine as long as you don't cut that character in half, or try to inspect its character code without doing the proper incantations[1].)

So, I guess what I'm asking is, at what point does the string become "internal", such that the engine will replace the character with the replacement character?

[1]: As given in the article you linked to.

[Kaworu]

I dare not try and reexplain the discussion in this bug report as my understanding feels insufficient, but the entire discussion at http://code.google.com/p/v8/issues/detail?id=761#c14 (note, I've linked to the 14th commment in the discussion, but there's more interesting stuff above) talks about it. At the core is a distinction between v8's internal representation of strings and it's API vs. what a browser engine which embeds v8 might do.