Unicode character sets & encoding in browsers

I'm trying to find out how character sets/encoding are implemented in browsers, specifically Unicode.

1. Are sets/encodin开发者_StackOverflow社区gs implemented separately in each browser or is it OS specific?
2. Is it possible to find out what version of the Unicode Character Db (UCD) is being used?
3. How are UCD updates pushed to each browser/OS? (Is it ever pushed out via automatic updates or is it just set for whatever version browser/OS you're using?)
4. Links to character sets/encoding information for each browser/OS manufacturer would be nice.

Thanks

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I don't believe the browsers worry about the UCD at all.

A wellformed page will have a charset defined for it. Example:
<meta http-equiv="Content-Type" content="application/xhtml+xml; charset=UTF-8" />

Any text that is being displayed will have a list of fonts defined for it (in preferred order). Example:
p { font-family: Verdana, Arial, sans-serif; }

For any character on the page the browser simply looks up the glyph in the font definition. If there isn't one it moves to the next font in the list. If it lucks out completely it probably just uses whatever uber-font the OS provides (Arial).