The HTML Math working group set out to design <<a notation for maths on the web>> rather than <<an XML DTD for mathematics>> or, by contrast, <<a web-portable dialect of TeX>>. This is a difference of emphasis from, for example, the ISO 12083 work which is more DTD oriented. XML was chosen for standardisation, acceptance and tool availability. However, using XML raises a number of issues.
Firstly, XML syntax leads to verbose encodings.
Operator elements in MathML content markup are canonically empty; this implies a logical difference between and, more significant than a simple absence of data.<fn><fn> and <fn/>, much more significant than a simple absence of data.
Name-case sensitivity in XML caused much discussion about whether to duplicate element names, allowing both upper- and lower-case forms: a proposal eventually dropped in favour of lowercase only.
Although XML provided all the tools needed to define a carrier format for mathematical expressions, an XML DTD is not enough to define all MathML validation rules. A sample issue is data-typing - MathML needs to define the content of something as numeric. Therefore there is a layer of MathML validation above the base XML syntax.
Contact Robin Cover with corrections and updates, or to submit contributions to the ISUG online document database.
