In addition to the Unicode Characters so far listed, one may use the combining characters U+0338 (/), U+20D2 (|) and U+20E5 (\) to produce negated or canceled forms of characters. A combining character should be placed immediately after its base character, with no intervening markup or space, just as is the case for combining accents.

In principle, the negation characters may be applied to any Unicode character, although fonts designed for mathematics typically have some negated glyphs ready composed. A MathML renderer should be able to use these pre-composed glyphs in these cases. A compound character code either represents a UCS character that is already available, as in the case of U+003D U+0338 which amounts to U+2260, or it does not as is the case for U+2202 U+0338. The common cases of negations, of the latter type, that have been identified are listed in the tables.

Note that it is the policy of the W3C and of Unicode that if a single character is already defined for what can be achieved with a combining character, that character must be used instead of the decomposed form. It is also intended that no new single characters representing what can be done by with existing compositions will be introduced. For further information on these matters see the Unicode Standard Annex 15, Unicode Normalization Forms , especially the discussion of Normalization Form C.

Unicode attempts to avoid having several character codes for simple font variants. For a code point to be assigned there should be more than a nuance in glyphs to be recorded. To record variants worth noting there is a special character in Unicode 3.2, U+FE00 (VARIATION SELECTOR-1), which acts as a postfix modifier. However the legally allowed combinations with this variation selector are restricted to a list recorded as part of Unicode. The VARIATION SELECTOR-1 character may only be applied to the characters listed here. The resulting combination is not regarded by Unicode as a separate character, but a variation on the base character. Unicode aware systems may render the combination as the base if the available fonts do not support the variant glyph shape.

Special Considerations Epsilon

Historically there has been much confusion and lack of agreement over variant forms for lower case epsilon.

This specification uses the definitions below. Note that the name epsilon is used for the character used in textual Greek (U+03B5) and varepsilon used for the epsilon symbol character more commonly used in mathematics (U+03F5). Note that this usage is compatible with the naming of similar pairs of characters (for example theta, vartheta) but incompatible with the naming convention used in TeX, MathML2 and some earlier mappings of the ISO entity sets to Unicode.

Phi

The situation for phi is very similar to that of epsilon, although with the further complication that early versions of Unicode had the sample glyphs for U+03C6 and U+03D5 in swapped from the current usage, and some older fonts still in use follow that older convention. The definitions used in this specification are as listed below.

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.

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 ligature 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 this entity is made from 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 noticable 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 , it is unadvisable 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 three cases shown above 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.

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 to U+29DA, is now assigned to 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 bow 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.

The following entity definitions have changed at this draft:

phi, lang, rang, OverParenthesis, UnderParenthesis, OverBrace, UnderBrace, lbbrk, rbbrk.

Differences between the XHTML entity definitions described here and the entity set described in the XHTML 1.0 DTD.

The differences between MathML 2 and the current entity definitions are listed below.

The following bracket symbols have been added to the Mathematical symbols block in Unicode versions between 3.1 and 5.1. MathML2 used similar characters intended for CJK punctuation.