I have a working solution, but I don't think it makes good use of the language.

The years right now extend from 1842 through 1862.

I tried
<xsl:for-each select="1842 to 1862">
     <tr><td><xsl:value-of select="."/></td>
     <td>
        <xsl:apply-templates select="documents/document[year = . and
contains(title, 'Selectmen')"/>
    </td>
    <td>
        <xsl:apply-templates select="documents/document[year = . and
contains(title, 'School')"/>
    </td>
    </tr>
</xsl:for-each>

The template that matches document just displays the value of each
title element followed by a <br />

But, I get an error that I can't use documents in that way because the
context is atomic.

I was able to get the following to work, basically hand-coding one row
for each of the year values.

<tr><td>1859</td>
      <td><xsl:apply-templates select="documents/document[year = 1859
and contains(title, 'Selectmen')]"/></td>
      <td><xsl:apply-templates select="documents/document[year = 1859
and contains(title, 'School')]"/></td>
</tr>

(repeat this for each year)

But there must be a direct way to do this with the language.

  <xsl:variable name="docs" select="documents/document"/>
  <xsl:for-each select="1842 to 1862">
     <tr><td><xsl:value-of select="."/></td>
     <td>
        <xsl:apply-templates select="$docs[year = . and
contains(title, 'Selectmen')"/>
    </td>
    <td>
        <xsl:apply-templates select="$docs[year = . and
contains(title, 'School')"/>
    </td>
    </tr>
</xsl:for-each>

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