xsl for-each: add code block every n rows?

Question

I am trying to transform a bit of xml which represents an image gallery into an html table. (it must be done with html and not with css). How do I add the row break </tr><tr> every six or so columns with xsl?

I have this:

<xsl:for-each select="//email/gallery" >
<td>
    <img>
    <xsl:attribute name="src">
        <xsl:value-of select="gallery-image-location"/>
    </xsl:attribute>
    <xsl:attribute name="alt">
        <xsl:value-of select="gallery-image-alt"/>
    </xsl:attribute>
    </img>
</td>
<xsl:if test="????">
    </tr>
    <tr>
</xsl:if>
<xsl:for-each>

In Javascript I would do something like:

for (i=0; i<gallery.length; i++) {
    htm += '<td><img src="' +
    gallery[i].gallery-image-location +
    '" alt="'+ gallery[i].gallery-image-alt +'"></td>';

    if (i%6 == 5 && i != gallery.length-1) {
        htm += '</tr><tr>';
    }
}

Answer 1

How do I add the row break every six or so columns with xsl?

In XSLT you don't!

XSLT processes nodes, not tags.

Here is the XSLT way of positional grouping:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>
 <xsl:strip-space elements="*"/>

 <xsl:template match="gallery[position() mod 6 = 1]">
  <tr>
   <xsl:apply-templates mode="proc"
        select=".|following-sibling::gallery[not(position() > 5)]"
   />
  </tr>
 </xsl:template>

 <xsl:template match="gallery" mode="proc">
  <td>
    <img src="{gallery-image-location}" alt="{gallery-image-alt}"/>
  </td>
 </xsl:template>

 <xsl:template match="gallery[not(position() mod 6 = 1)]"/>
</xsl:stylesheet>

when this transformation is applied on the following XML document:

<email>
    <gallery>
        <gallery-image-location>http://server/picts/1</gallery-image-location>
        <gallery-image-alt>Description 1</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/2</gallery-image-location>
        <gallery-image-alt>Description 2</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/3</gallery-image-location>
        <gallery-image-alt>Description 3</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/41</gallery-image-location>
        <gallery-image-alt>Description 4</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/5</gallery-image-location>
        <gallery-image-alt>Description 5</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/6</gallery-image-location>
        <gallery-image-alt>Description 6</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/7</gallery-image-location>
        <gallery-image-alt>Description 7</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/8</gallery-image-location>
        <gallery-image-alt>Description 8</gallery-image-alt>
    </gallery>
    <gallery>
        <gallery-image-location>http://server/picts/9</gallery-image-location>
        <gallery-image-alt>Description 9</gallery-image-alt>
    </gallery>
</email>

the wanted, correct result is produced:

<tr>
    <td>
        <img src="http://server/picts/1" alt="Description 1"/>
    </td>
    <td>
        <img src="http://server/picts/2" alt="Description 2"/>
    </td>
    <td>
        <img src="http://server/picts/3" alt="Description 3"/>
    </td>
    <td>
        <img src="http://server/picts/41" alt="Description 4"/>
    </td>
    <td>
        <img src="http://server/picts/5" alt="Description 5"/>
    </td>
    <td>
        <img src="http://server/picts/6" alt="Description 6"/>
    </td>
</tr>
<tr>
    <td>
        <img src="http://server/picts/7" alt="Description 7"/>
    </td>
    <td>
        <img src="http://server/picts/8" alt="Description 8"/>
    </td>
    <td>
        <img src="http://server/picts/9" alt="Description 9"/>
    </td>
</tr>