RE: BaseChar problem in XML 1.0?

I believe the choice was made to avoid "ambiguous" identifiers, i.e. ones
that you cannot unambiguously re-type if you see them.
 
Imagine the identifier VISIBLE.  Is that "V", then "I", then "S" etc. or
"VI" (U+2165), then "S", then "I" (U+2160), etc. ?  Ambiguous. Out go all
the Roman numerals from 2610 to 217F.  No such problem for 2180-2182, the
glyphs are distinct enough (same for U+2183, but it wasn't around when XML
1.0 was designed).
--
François Yergeau 

-----Message d'origine-----
De : Andy Heninger [mailto:heninger@us.ibm.com]
Envoyé : 5 février, 2001 13:09
À : xml-editor@w3.org
Cc : Glenn Marcy; Arnaud Le Hors
Objet : BaseChar problem in XML 1.0?



Hello XML Editors, 

Here's a question that just came up regarding the definition 
of allowable identifier characters in XML. 

From the XML spec, 

Production [85]  BaseChar includes the characters [#x2180-#x2182].   

These are Roman Numerals 
    1000    CD 
    5000    (No reasonable ASCII approximation) 
   10000    (No reasonable ASCII approximation) 

BaseChar does not include the remaining Unicode Roman Numerals, 
which encompass the range [#x2160-#x2183] 

I checked with Mark Davis, and there is nothing from a 
Unicode perspective that sets the three included characters 
apart from the rest of the Unicode Roman Numerals.  It would 
seem that they either all ought to be allowed or disallowed as 
BaseChars. 

Unicode's recommendations for Identifier characters allow them 
all. 

Something does not seem right.  Is there some logic here 
that escapes me, or is it possible that the inclusion of 
these characters is an editing error, or ??? 

  

 -- Andy Heninger,      IBM Cupertino, XML Technology Group
     heninger@us.ibm.com