xsl:fallback

Provides fallback behavior when the surrounding instruction is not recognized by the processor.

<xsl:some-future-instruction>
  <xsl:fallback>
    <xsl:message>not supported</xsl:message>
  </xsl:fallback>
</xsl:some-future-instruction>

If a stylesheet is processed by an XSLT processor that doesn’t know about a given instruction, that instruction’s body is normally an error. By placing an xsl:fallback child inside, the stylesheet can supply a workaround that runs when the parent is unknown. If the parent is recognized, xsl:fallback is ignored.

This makes stylesheets forward-compatible: an XSLT 4.0 instruction can be used together with an xsl:fallback containing an XSLT 3.0 alternative.

Attributes

None.

Example

Polyfilling a hypothetical instruction:

<xsl:future-format value="$x">
  <xsl:fallback>
    <xsl:value-of select="format-number($x, '#,##0.00')"/>
  </xsl:fallback>
</xsl:future-format>