# 3.10.7.1.4 `<equation-number>`

Use the `<equation-number>`

element to indicate that a block
equation is numbered and, optionally, to specify the number to use for the block equation.

When the `<equation-number>`

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

element has non-whitespace-only
content the content SHOULD be used as
the equation number. For explicit numbers the content of the element SHOULD be the number value without any
surrounding punctuation, for example, "3.2a" rather than "(3.2a)". Processors SHOULD add punctuation or decoration to
the number as appropriate.

In normal usage a block equation will have at most one number. However,
`<equation-number>`

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

, for example, to allow numbers with different (and
exclusive) conditional properties.

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

## Content models

See appendix for information about this element in OASIS document type shells.

## Inheritance

+ topic/ph equation-d/equation-number

## Example

```
<p>A block equation using an image:</p>
<equation-block id="eq-001">
<equation-number/>
<image keyref="equation-image-01">
<alt>a squared plus b squared.</alt>
</image>
</equation-block>
```

```
<p>A block equation using an image:</p>
<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>
```

## Attributes

The following attributes are available on this element: Universal attribute group and outputclass.