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.

## 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.