Why is //*[1] different from (//*)[1]

StackOverflow https://stackoverflow.com/questions/22931354

  •  29-06-2023
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質問

I created two files, input.xml and formatter.xslt.

input.xml:

<?xml-stylesheet type="text/xsl" href="formatter.xslt"?>
<div><span>1</span><span>2</span></div>

formatter.xslt:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
        <html><head></head><body>
            <xsl:copy-of select="//*[1]"/>
            ,
            <xsl:copy-of select="(//*)[1]"/>
        </body></html>
    </xsl:template>
</xsl:stylesheet>

Then I opened input.xml in Internet Explorer, and pressed F12. I saw the DOM tree was like:

<html><head></head><body>
    <div><span>1</span><span>2</span></div><span>1</span>
    ,
    <div><span>1</span><span>2</span></div>
</body></html>

Why did //*[1] and (//*)[1] copy different elements into the output document?

役に立ちましたか？

解決

Well //*[1] is /descendant-or-self::node()/*[1] while (//*)[1] is (/descendant-or-self::node()/*)[1] so the former selects all element nodes that are the first child of their parent while the latter selects only the first node selected by the expression in parentheses, that is it selects only the first of those element nodes that are a child of a parent node.

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