Re: Whitespace characters in Unicode

From: Sean Leonard <>
Date: Fri, 5 Aug 2016 08:52:56 -0700

Here are specific questions (perhaps Mark Davis, but anyone really with
experience, can respond):

As Mark said, there are 25 whitespace characters. (I forgot to include
HT, so that makes 25 from my original post.)

What makes a character a "whitespace" in Unicode, e.g., why are ZWSP and
ZWNBSP not "whitespace" even though they clearly say "SPACE" in them?

What are "Unicode-y" ways to compute word boundaries? Related to prior
question--I suppose ZWSP is not "whitespace", but like whitespace, it
separates words. I suppose that since it is not printable, it is
"confusing", and therefore should be avoided in contexts where the
printed representation of Unicode code points matters.

Why is Pattern_White_Space significantly disjoint from White_Space,
namely, why does Pattern_White_Space include LTRM and RTLM (and notably
LS and PS) yet omit the spaces U+1680 and in the U+2000 range?

Any implementation experience from other standards authors/implementers
who have run into problems with shifty whitespace definitions?



On 8/4/2016 2:28 PM, Leonardo Boiko wrote:
> I'm sorry; I thought that, when you wanted to separate identifiers, it
> might be interesting to follow existing regexps definitions; this way
> your syntax would play along with already-existing tools (e.g. you'd
> be making it easy for someone to pipe your language into grep -P
> "\p{Whitespace}").
> But I was talking out of my depth; I've never worked with defining
> Unicode identifiers, so I'm not really qualified to answer. I'm sure
> Davis and the others can give better answers to your questions.
> Meanwhile, I see that UAX #31 goes further into Unicode identifiers.
> It says that Pattern_White_Space is stable (unlike Whitespace,
> perhaps?), and intended for use in regexp-like "patterns" which mix
> literal characters, whitespace, and syntax (special characters), where
> the latter two would e.g. require quoting. For example, Perl has a
> "/x" flag which makes unquoted Pattern_White_Space characters be
> ignored in regexpes (so that you can make then less illegible).
> However, UAX #31 it also gives a Default Identifier Syntax, which
> bounds identifiers not by Whitespace but by their start characters,
> identified by ID_Start, defined like this:
> |> ID_Start| characters are derived from the Unicode General_Category
> of uppercase letters, lowercase letters, titlecase letters, modifier
> letters, other letters, letter numbers, plus Other_ID_Start, minus
> Pattern_Syntax and Pattern_White_Space code points.
> So it makes reference only to Pattern_White_Space and not Whitespace.
> On the other hand, I guess the listing above will exclude Whitespace
> characters, since they don't count as any of letters, numbers, or
> Other_ID_Start?
> None of that is guaranteed to be stable, though. UAX #31 includes a
> separate definition for "Immutable identifiers", which are, and
> suggests various compromises between them.
> 2016-08-04 17:44 GMT-03:00 Sean Leonard <
> <>>:
> I read through mainly says that <space> == \s ==
> \p{Whitespace} == property White_Space is true. Does it say
> anything else or more significant than that, that I'm missing?
> Sean
> On 8/4/2016 1:17 PM, Leonardo Boiko wrote:
>> What Mark Davis said; also, depending on what you need, consider
>> taking a look at the definitions used by Unicode regexpes, at
>> <> .
>> 2016-08-04 16:37 GMT-03:00 Sean Leonard
>> < <>>:
>> Hi Unicode Folks:
>> I am trying to come up with a sensible sets of characters
>> that are considered whitespace or newlines in Unicode, and to
>> understand the relative stability policy with respect to
>> them. (This is for a formal syntax where the definition of
>> "whitespace" matters, e.g., to separate identifiers, and I
>> want to be as conservative as possible.) Please let me know
>> if the stuff below is correct, or needs work.
>> The following characters / sequences are considered line
>> breaking characters, per UAX #14 and Section 5.8 of UNICODE:
>> So, basically: U+000A-U+000D, U+0085, U+2028, U+2029, and the
>> combination U+000D U+000A (treated as one line break). These
>> characters / sequences are called "newlines".
>> There will not be any additional code points that are
>> assigned to be line breaks. (Correct?)
>> CRLF, CR, LF, and NEL are also considered "newline functions"
>> or NLF. These are distinguished from other codes (above) that
>> also mean line breaks, mainly because of historical and
>> widespread use of them.
>> There are several formatting characters that affect word
>> wrapping and line breaking, as discussed in those
>> documents...but they are not line breaking characters.
>> ****
>> The following characters are whitespaces: characters (code
>> points) with the property WSpace=Y (or White_Space). This is:
>> newlines
>> U+0020 U+00A0 U+1680 U+2000-200A U+202F U+205F U+3000
>> Assigned characters that are not listed above, can never be
>> whitespace (according to Unicode). However, the set is not
>> closed, so unassigned code points *could* be assigned to
>> whitespace. It is (unlikely? very unlikely? Pretty much never
>> going to happen?) that additional code points will be
>> assigned to whitespace.
>> ****
>> There are some other characters that Unicode does not
>> consider whitespace, but deserve discussion:
>> <>
>> <>
>> *These appear in Pattern_White_Space, but Pattern_White_Space
>> excludes U+2000-200A characters, which are obviously spaces.
>> This is confusing and I would appreciate clarification /why/
>> Pattern_White_Space is significantly disjoint from White_Space.
>> ********
>> The borderline characters above are not considered WSpace=Y,
>> but sometimes might have space-like properties. ZWP and ZWNBP
>> are obviously "space" characters, but they never generate
>> whitespace. I suppose that conversely LTRM and RTLM are
>> obviously "not space" characters, but they could generate
>> whitespace under certain circumstances. Ditto for other
>> formatting characters in general (for which the class is much
>> larger).
>> Therefore I guess a Unicode definition of "whitespace" (or
>> "space characters") is: an assigned code point that *always*
>> (is supposed to) generates white space (empty space between
>> graphemes).
>> ********
>> Are there other standards that Unicode people recommend, that
>> have addressed whether certain borderline characters are
>> considered whitespace vs. non-whitespace (e.g., possibly
>> acceptable as an identifier or syntax component)?
>> Regards,
>> Sean
Received on Fri Aug 05 2016 - 10:55:43 CDT

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