How to loop through a non-nested XML structure?

Question

PHP

How in XSL to display such a set of tags one by one through a loop? Tags can be unlimited.

<main>
  <tag ROWNUM="1">Олег</tag>
  <tag ROWNUM="2">Виктор</tag>
  <tag ROWNUM="3">Денис</tag>
  <tag ROWNUM="4">Кирилл</tag>
  <tag ROWNUM="1">Олегович</tag>
  <tag ROWNUM="2">Викторович</tag>
  <tag ROWNUM="3">Денисович3</tag>
  <tag ROWNUM="4">Кириллович</tag>
</main>

So that it was "Oleg Olegovich, Viktor Viktorovich, Denis Denisovich" ...?
There used to be a nested structure and parsed through for-each. Now the sign of the group is in ROWNUM and everything is in one tag

Answer 1

I asked myself - I answered it myself =) With stackoverflow
XSLT 1.0. Three options.
Following-sibling is used twice, which is ugly and wasteful.

<xsl:for-each select="//tag[@ROWNUM = following-sibling::tag/@ROWNUM]">
    <name>
        <xsl:value-of select="."/>
        <xsl:variable name="rownum" select="@ROWNUM"/>
        <xsl:value-of select="./following-sibling::tag[@ROWNUM = $rownum]"/>
    </name>
</xsl:for-each>

We use the key. And two cycles, which is also inelegant.

<xsl:for-each select="//tag[@ROWNUM = following-sibling::tag/@ROWNUM]/@ROWNUM">
    <name>
        <xsl:for-each select="key('num', .)">
            <xsl:value-of select="."/>
        </xsl:for-each>
    </name>
</xsl:for-each>

We use the key again. Instead of the second loop, we use index access.

<xsl:for-each select="//tag[@ROWNUM = following-sibling::tag/@ROWNUM]/@ROWNUM">
    <name>
        <xsl:value-of select="key('num', .)[1]"/>
        <xsl:value-of select="key('num', .)[2]"/>
    </name>
</xsl:for-each>