Characters that should be displayed?

James Clark jjc at
Mon Jun 30 08:37:23 CDT 2014

A couple of your questions are addressed by:

In particular:

Q: Which characters should be displayed with a missing glyph, if not
A: All characters other than whitespace and default-ignorable characters.


On Mon, Jun 30, 2014 at 1:44 AM, Koji Ishii <kojiishi at> wrote:

> Hello Unicoders,
> I’m a co-editor of CSS Text Level 3[1], and I would appreciate your
> support in defining rendering behavior in CSS.
> The spec currently has the following text[2]:
> > 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. (As required by [UNICODE], unsupported Default_ignorable
> characters must also be ignored for rendering.)
> and there’s a feedback saying that CSS should display visible glyphs for
> these control characters. Since all major browsers do not display them
> today, this is a breaking-change and the CSS WG needs to discuss on this
> feedback. But the WG would appreciate to understand what Unicode recommends.
> I found the following text in Unicode 6.3, p. 185, "5.21 Ignoring
> Characters in Processing”[3]:
> > Surrogate code points, private-use characters, and control characters
> are not given the Default_Ignorable_Code_Point property. To avoid security
> problems, such characters or code points, when not interpreted and not
> displayable by normal rendering, should be displayed in fallback rendering
> with a fallback glyph
> By looking at this, my questions are as follows:
> 1. Should control characters that browsers do not interpret be displayed
> in fallback rendering?
> 2. Should private-use characters (U+E000-F8FF, 0F0000-0FFFFD,
> 100000-10FFFD) without glyphs be displayed in fallback rendering?
> These two questions are probably yes from what I understand the text
> quoted above, but things get harder the more I think:
> 3. When the above text says “surrogate code points”, does that mean
> everything outside BMP? It reads so to me, but I’m surprised that
> characters in BMP and outside BMP have such differences, so I’m doubting my
> English skill.
> 4. Should every code point that are not given the
> Default_Ignorable_Code_Point property and that without interpretations nor
> glyphs displayed in fallback rendering? I could not find such statement in
> Unicode spec, but there are some people who believe so.
> 5. Is there anything else Unicode recommends to display in fallback
> rendering, or not to display? This must be RTFM, but pointing out where to
> read would be appreciated.
> Thank you for your support in advance.
> [1]
> [2]
> [3]
> /koji
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