Used to allow conditional content construction to be made streamable. Outputs the enclosed content only if the containing sequence generates no "ordinary" content.

If the instruction appears in a sequence constructor, it must come after all other instructions.

Although intended primarily to make streaming applications easier to write, the instruction can also be handy irrespective of streaming to avoid evaluating complex conditions more than once.

Category: instruction
Content: sequence-constructor
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element




Notes on the Saxon implementation

New in XSLT 3.0, and implemented since Saxon 9.7.


The following code generates substitute text when there is no content, however it is not guaranteed-streamable because it processes child item-for-sale elements more than once:

<xsl:apply-templates select="item-for-sale"/> <xsl:if test="empty(item-for-sale)"> <p>There are no items for sale.</p> </xsl:if>

To make this streamable, it can be rewritten using the xsl:on-empty instruction:

<xsl:sequence> <xsl:apply-templates select="item-for-sale"/> <xsl:on-empty> <p>There are no items for sale.</p> </xsl:on-empty> </xsl:sequence>

Links to W3C specifications

XSLT 3.0 Specification

See also