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 <[email protected]>: > I read through TR18...it 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 > http://unicode.org/reports/tr18/ . > > 2016-08-04 16:37 GMT-03:00 Sean Leonard <[email protected]>: > >> 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: >> >> CRLF CR LF FF VT NEL LS PS >> >> 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: >> U+180E MONGOLIAN VOWEL SEPARATOR: <https://codeblog.jonskeet.uk/ >> 2014/12/01/when-is-an-identifier-not-an-identifier-attack- >> of-the-mongolian-vowel-separator/> >> <https://codeblog.jonskeet.uk/2014/12/01/when-is-an-identifier-not-an-identifier-attack-of-the-mongolian-vowel-separator/> >> U+200B ZERO WIDTH SPACE >> U+200C ZERO WIDTH NON-JOINER >> U+200D ZERO WIDTH JOINER >> U+200E LEFT-TO-RIGHT MARK* >> U+200F RIGHT-TO-LEFT MARK* >> U+2060 WORD JOINER >> U+FEFF ZERO WIDTH NON-BREAKING SPACE >> >> *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 >> > > >
