Mathematics can be inserted into an article in four ways:
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unnumbered display format
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numbered display format
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Informal Text Markup
The use of over/under displays, and other complex relationships in inline math objects will require the complete structures explained below. However, it is perfectly acceptable to submit simple math statements within text as strings of character entities, using the rules for entity usage defined elsewhere. But proper spacing around operators is required at all times, with entity usage or with normal Latin text and numbers.
Formal Math Constructs
All three of the formal constructs directly or indirectly hold an <equation> element:
<inlinematheqn><equation>...<equation></inlinematheqn>
<matheqn><equation>...</equation></matheqn>
<unnummatheqn><equation>...</equation></unnummatheqn>
The first of these constructs encloses an inline formula, while the others enclose one or more display formulae, with or without numbered labels.
Multiple Display Formulae
There are two techniques available for capturing multiple display formulae. The first is simply to use multiple display-level elements (numbered or unnumbered). The second is to use a single multi-part "compound" wrapper:
<matheqn><equation>...<equation></matheqn>
<matheqn><equation>...</equation></matheqn>
<matheqn>
<mathcompound><equation>...</equation><equation>...</equation><mathcompound>
</matheqn>
However, the "compound" technique should be avoided if possible, because it presents rendering and linking challenges in electronic products.
Three Data Formats
The formal content model for math allows for storage of three separate forms which may coexist. The equation can be shown as an image, using TeX markup, and using MathML markup:
<equation>
<texstructure>
<?TeX c_{ij}^m c_{mk}^l + ... = 0. ?>
</textstructure>
<graphic linkend="ILM004"/>
<formula>
<?MathML <math><mrow><msubsup><mi>c</mi><mrow><mi>i</mi>...</math> ?>
</formula>
</equation>
Note that the TeX and MathML markup are both embedded in XML processing instructions. For this reason, the MathML module is not needed in the main DTD.