xsl:on-non-empty

Description

xsl:on-non-empty is the complement of xsl:on-empty. Its content is output only when the other instructions in the same sequence constructor have produced at least one node. If no nodes were produced, xsl:on-non-empty is silently suppressed.

The classic use case is a conditional heading or section wrapper that should only appear when there is actual content beneath it. Before XSLT 3.0 this required storing the content in a variable, testing whether it was non-empty, and then wrapping it — three steps. With xsl:on-non-empty you can express the heading inline, adjacent to the content that conditions it.

Like xsl:on-empty, this element is evaluated after its preceding siblings in the same sequence constructor have been processed. It considers any node — including whitespace text nodes — as “non-empty” content.

The three streaming-content elements (xsl:on-empty, xsl:on-non-empty, and xsl:where-populated) are often used together. xsl:on-non-empty belongs at the start of a sequence when the conditional content (such as a heading) must appear before the main content it guards.

Attributes

xsl:on-non-empty has no element-specific attributes. It contains a sequence constructor.

Examples

Conditional section header before content

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<report>
  <errors>
    <error>Disk quota exceeded</error>
    <error>Network timeout</error>
  </errors>
</report>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="html" indent="yes"/>

  <xsl:template match="/report">
    <div>
      <!-- Header appears only if there are errors -->
      <xsl:on-non-empty>
        <h2>Errors found</h2>
      </xsl:on-non-empty>
      <xsl:apply-templates select="errors/error"/>
    </div>
  </xsl:template>

  <xsl:template match="error">
    <p class="error"><xsl:value-of select="."/></p>
  </xsl:template>
</xsl:stylesheet>

Output:

<div>
  <h2>Errors found</h2>
  <p class="error">Disk quota exceeded</p>
  <p class="error">Network timeout</p>
</div>

Combined on-non-empty and on-empty

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/inventory">
    <stock>
      <xsl:on-non-empty>
        <summary>Items in stock:</summary>
      </xsl:on-non-empty>
      <xsl:apply-templates select="item[@qty > 0]"/>
      <xsl:on-empty>
        <summary>No items currently in stock.</summary>
      </xsl:on-empty>
    </stock>
  </xsl:template>

  <xsl:template match="item">
    <entry qty="{@qty}"><xsl:value-of select="@name"/></entry>
  </xsl:template>
</xsl:stylesheet>

Notes

• xsl:on-non-empty must be evaluated by the processor after the preceding siblings. Processors that buffer content do so internally; the order in the output is still as written.
• Like xsl:on-empty, it evaluates the preceding sibling nodes in the same sequence constructor only — not the wider result tree.
• This element is streamable and works well inside streaming templates.
• Whitespace-only text nodes produced by sibling instructions are counted as non-empty content.

See also

• xsl:on-empty
• xsl:where-populated