Math Alphabets

Displaying Math Alphabets

• Can use Unicode surrogate pair mechanisms available on OS
• Alternatively, bind to standard fonts and use corresponding BMP characters
• Second approach probably faster and to display Unicode one needs font binding in any event. But most traditional fonts are not suited to math alphabetic characters
• A single math font may look more consistent

The question arises as to how to implement the mathematical alphanumeric characters. One approach uses a dedicated math font along with Unicode surrogate pair support from the operating system.

This approach has a couple of advantages:

1. the characters can be designed as a group to look good with one another, and
2. relatively little effort is needed in the math display engine.

Alternatively, the math display engine can bind the math alphanumerics to standard fonts and use corresponding BMP characters. This approach may have faster performance (depending on how efficiently the operating system handles surrogate pairs). Font binding is an extra step, but it may already be available, since in general to display Unicode it's necessary to have a font binding facility of some kind. Mathematical variables are most commonly set in a serifed form of italics, but not all italic fonts can be used successfully. In common text fonts, the italic letter v and Greek letter nu are not very distinct. A rounded italic letter v is therefore preferred in a mathematical font. There are other characters that sometimes have similar shapes and require special attention to avoid ambiguity. Character spacing is also different in mathematical expressions and in ordinary text.

Math Alphabetics via Glyph Variants

• One approach to the math alphanumerics would be to use a set of math glyph variant selectors
• Such a tag would follow a base character imparting a math style
• Approach was dropped since it seemed likely to be abused
• One math variant selector does exist to offer a different line slant for some composite symbols
• Other variant selectors are being defined for nonmath purposes, e.g., Han variants

Another way to represent math alphanumerics in plain text would be to use math variant tags that follow the appropriate base characters. This approach is more general than outright encoding since the variant tags could follow any characters in the BMP. However only certain characters should be eligible for these math styles, so one would have to have tables defining which combinations are legal and which should be discarded or ignored. The approach was dropped because it was felt that it could be abused too easily for non-math, rich-text purposes that would be better handled using mark up.

One math variant selector (U+FE00) was introduced to get a different line slant for some composite symbols, most notably in the context of negation. Ordinarily negated math symbols have a forward slash overlay, but a vertical slash overlay is used as well and may have different semantics from the forward slash.