`<equation-number>`

The `<equation-number>`

element indicates
that a block equation should be numbered. It
optionally specifies the number to use for the block
equation.

## Usage information

In normal usage, a block equation has a single number. However,
the `<equation-number>`

element can occur
multiple times within the `<equation-block>`

element. This enables the use of numbers with different (and
exclusive) conditional properties.

When the `<equation-figure>`

element contains
content, the content of the element should be the number value
without any rendering-specific punctuation,
for example, 3.2a rather than
(3.2a).

## Rendering expectations

In this context, white-space content is considered equivalent to
empty content. When the `<equation-number>`

element has empty content, the equation number SHOULD be generated. When the
`<equation-number>`

element is not empty,
the content SHOULD be used as
the equation number. Processors MAY add punctuation or decoration to the number.

The details of equation numbering and number presentation are processor-specific. A common practice is to present the equation number to the right of the equation, centered vertically within the vertical extent of the block equation.

## Specialization hierarchy

The `<equation-number>`

element is specialized from
`<ph>`

. It is defined in the equation domain module.

## Attributes

The following attributes are available on this element: universal attributes.

## Examples

This section contains examples of how the
`<equation-number>`

element can be used:

The following code sample shows how an
`<equation-number>`

element can specify the
value for an equation number:

```
<equation-block id="eq-3.2a">
```**<equation-number>3.2a</equation-number>**
<image keyref="equation-image-01">
<alt>a squared plus b squared.</alt>
</image>
</equation-block>