[css-text] Control characters

CSS Text says:

Control characters (Unicode class Cc) other than tab (U+0009), line feed
> (U+000A), and carriage return (U+000D) are ignored for the purpose of
> rendering.


(This is a change from CSS 2.1, which says they are rendered as usual.) I
was wondering what the thinking is here.  This requirement conflicts with
Unicode (see http://www.unicode.org/faq/unsup_char.html) in a couple of
ways:

1. In addition to 0x9, 0xA and 0xD, Unicode gives characters 0xB (VT), 0xC
(FF) and 0x85 (NEL) the White_Space property.  Characters with the
White_Space property are supposed to be rendered as a visible but blank
space. (Of these, HTML includes only 0xC as a space character.)

2. Other control characters are supposed to be rendered normally (ie
displayed with a missing glyph if not available in the font).

James