A Special Considerations
A.3 Multiple Character Entities
In addition to the combining and variant character combinations listed in the previous sections, the following table lists the remaining entity replacement texts that consist of more than one character.
| Entity | Set | Description | Unicode Character | ||
|---|---|---|---|---|---|
| fjlig | isopub | small fj ligature | U+0066 U+006A |  | fj ligature |
| ThickSpace | mmlextra | space of width 5/18 em | U+205F U+200A |  | space of width 5/18 em |
| race | isoamsb | reverse most positive, line below | U+223D U+0331 |  | REVERSED TILDE with underline |
| acE | isoamsb | most positive, two lines below | U+223E U+0333 |  | INVERTED LAZY S with double underline |
| DownBreve | mmlextra | breve, inverted (non-spacing) | U+0020 U+0311 |  | COMBINING INVERTED BREVE |
| tdot | isotech | three dots above | U+0020 U+20DB |  | COMBINING THREE DOTS ABOVE |
| TripleDot | mmlalias | alias ISOTECH tdot | |||
| DotDot | isotech | four dots above | U+0020 U+20DC |  | COMBINING FOUR DOTS ABOVE |
Unicode does not have an fj character, although the other common f ligatures such as fi (U+FB01) are contained in the Alphabetic Presentation Forms block. The fjlig entity is mapped to the pair of characters "fj"; modern typesetting engines should automatically use the fj ligature for this combination if the font supplies such a ligature.
Unicode has a range of space characters (including all multiples of 1/18 em up to 6/18, except for 5/18 em) thus the ThickSpace entity is mapped to a pair of space characters. An alternative would have been to use U+2005 (1/4 em), but 1/4 em is not equal to 5/18 em, so the above definition was chosen, despite the fact that the difference is unlikely to be visibly noticeable at most typeset font sizes.
The entities race and acE denote underlined characters for which Unicode does not have codepoints, thus combining underline characters have been used, in a way analogous to the use of combining strokes for negated operators.
For reasons explained further in [Charmod-norm], it is not advisable to to start the replacement text of an entity with a combining character, as then potentially different results may be produced depending on the order in which entity expansion and Unicode normalisation are performed. As far as possible this specification uses non-combining characters, however, in the cases tdot, TripleDot and DotDot Unicode only has combining forms of the accents, and so the entity replacement text starts with a space, to avoid the possibility that the expansion of the entity combines with preceding text.
B Changes
B.1 Changes since 2014-04-10 (Second Edition Recommendation)
Source files updated to Unicode 8.0, affecting the character tables, but with no changes to generated entity files or stylesheets.
B.2 Changes between 2010-04-01 and 2014-04-10 (First and Second Edition Recommendations)
Source files updated to Unicode 6.3, affecting the character tables, but with no changes to generated entity files or stylesheets.
Source files updated Unicode 6.1 data on Arabic math alphabets (U+1EE??). Additional tables shown in Sections 3 and 4.
Section 2 Sets of names reorganized to highlight the htmlmathml set which is used in MathML and HTML. Also link to XSL and JSON formats for the HTML MathML set.
B.3 Changes between 2010-04-01 and 2010-02-11
Several example images improved, bringing them more in line with the Unicode reference images.
B.4 Changes between 2010-02-11 and 2009-11-17
Various editorial improvements, including using Unicode U+1234 notation more consistently rather than displaying the internal IDs of the form U01234.
The combined entities file distributed with the 2009-11-17 draft introduced an error that if two entity names differed only by case, only one was included. This has been corrected.
The combined entity set htmlmathml corresponding to the entities usable in HTML and MathML is now explicitly provided. The predefined set, corresponding to the entities predefined in XML is now documented (it was previously used internally).
The entities xvee and xwedge had the correct Unicode assignments (U+22C1 and U+22C0) but the entity descriptions have been swapped, xvee is logical or and xwedge is logical and. This error in [ISO9573-13-1991] was reported in 1999, in a Proposed Technical Corrigendum, but not previously fixed. The entity files are unaffected by this change.
The entity NotGreaterFullEqual which had been erroneously assigned to a negated less than operator (U+2266 U+0338) has been corrected to be the negated greater than operator (U+2267 U+0338).
A sample catalog is now provided to redirect references to the entity files to copies on the local machine rather than the W3C server.
B.5 Changes between 2009-11-17 and 2008-07-21
The html5-uppercase set is now documented.
The entities ohm and angst have changed to U+03A9 and U+00C5 to match NFC. See w3c bugzilla entry.
The entity race, which had been erroneously assigned U+29DA, is now assigned the combination U+223D U+0331. (U+223D isn't quite the shape shown in the original ISO document which is a rotated S rather than a rotated tilde, but this appears to be the closest character in Unicode 5.2.)
The entities bsolhsub and suphsol which were previously mapped to two-character combinations U+005C U+2282 and U+2283 U+002F are now mapped to the Unicode 5 characters that were added specifically to support these entities, U+27C8 and U+27C9.
The source files have all been updated to match Unicode 5.2.
The entity ThickSpace now maps to the pair U+205F U+200A rather than the triple U+2009 U+200A U+200A (4/18 + 1/18)em rather than (3/18 + 1/18 + 1/18)em.
The entity UnderBar maps to the spacing character _ rather than the combining character U+0332.
The entity OverBar maps to the spacing character U+203E (like the XHTML entity oline) rather than the macron character U+00AF.
The entities epsiv and varepsilon are now mapped to the epsilon symbol U+03F5 rather than being aliases for the entity epsilon, U+03B5.
The entities phiv and varphi are now mapped to the phi symbol U+03D5 rather than being aliases for the entity phi, U+03C6.