XSLT concatenation of tags

Question

I have this sample document:

<root>
    <span class="a">te</span><span class="a">st</span> <span class="a">tag</span>
    some other text
    <span class="b">keep</span>
</root>

I would like to have something like this:

<root>
    <span class="a">test tag</span>
    some other text
    <span class="b">keep</span>
</root>

Or at least this:

<root>
    <span class="a">test</span> <span class="a">tag</span>
    some other text
    <span class="b">keep</span>
</root>

There will be variable count of class="a" spans. Is it possible in XSLT?

EDIT

tried to solve:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*"/>
        </xsl:copy>
    </xsl:template>
    <xsl:template match="*/span[@class = 'a']"/>
    <xsl:template match="*/span[@class = 'a'][1]">
        <span class="a">
            <xsl:for-each select="../span[@class = 'a'] | ../text()[. = ' ']">
                <xsl:choose>
                    <xsl:when test=". = ' '">
                        <xsl:copy/>
                    </xsl:when>
                    <xsl:otherwise>
                        <xsl:value-of select="./text()"/>
                    </xsl:otherwise>
                </xsl:choose> 
            </xsl:for-each>
        </span>
    </xsl:template>
</xsl:stylesheet>

but when I have this input?

<root>
    <span class="a">te</span><span class="a">st</span> <span class="a">tag</span>
    some other text
    <span class="b">keep</span>
    <span class="a">te</span><span class="a">st</span> <span class="a">tag</span>
</root>

How to solve this?

Answer 1

The second variant can be achieved using:

XSLT 1.0

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

<xsl:key name="grp" 
         match="span[@class='a'][preceding-sibling::node()[1][self::span[@class='a']]]" 
         use="generate-id(preceding-sibling::span[@class='a'][not(preceding-sibling::node()[1][self::span[@class='a']])][1])" />

<!-- identity transform -->
<xsl:template match="@*|node()">
    <xsl:copy>
        <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
</xsl:template>

<xsl:template match="span[@class='a'][not(preceding-sibling::node()[1][self::span[@class='a']])]" priority="1">
    <span class="a">
        <xsl:for-each select=". | key('grp', generate-id())" >
            <xsl:value-of select="."/>
        </xsl:for-each>
    </span>
</xsl:template>

<xsl:template match="span[@class='a']"/>

</xsl:stylesheet>

With some more work, you could include the interspersing white-space only text nodes in the group. Alternatively, look at a technique known as "sibling recursion".