XSLT Selecting specific sibling nodes between two nodes of xml

Question

Suppose I have the following XML structure

<?xml version="1.0" encoding="UTF-8" ?>
<?xml-stylesheet type="text/xsl"?>
<?xml-stylesheet type="text/xsl"?>
<WTT>
<Msg 
    UserText="Iswritable = true" >
</Msg>
<Test 
   BaseLvl="Msg" >
</Test>
<start
   id = "1" >
</start>
<Msg 
   UserText="Iswritable = true" >
</Msg>
<Test 
   BaseLvl="Msg"  >
</Test>
<Msg 
   UserText="WriteBuffers = 2">
</Msg>
<Test 
   BaseLvl="Txt" >
</Test>
<Msg 
   UserText="ReadBuffers = 1">
</Msg>
<end
   id ="1" >
</end>

<start
   id = "2" >
</start>
<Test
   BaseLvl="sound" > 
</Test>
<Test 
   BaseLvl="Msg" >
</Test>
<Msg 
   UserText="vertexbuffers = 1">
</Msg>
<end
   id ="2" >
</end>
<Msg 
   UserText="vertexbuffers = 1">
</Msg>
</WTT>

Output :

<start
   id = "1" >
</start>
<Msg 
   UserText="Iswritable = true" >
</Msg>
<Msg 
   UserText="ReadBuffers = 1">
</Msg>
<end
   id ="1">
</end>
<start
   id = "2" >
</start>
<Msg 
   UserText="vertexbuffers = 1">
</Msg>
<end
   id ="2" >
</end>    

The structure of the xml is not fixed and any tag can be put anywhere. Is there a way to do this? I tried using foreach and selecting only msg nodes but we cannot break the foreach in xslt. I just have to select all the <msg/> tags between <start/> and the <end/> tags in separate groups.

Answer 1

The following stylesheet:

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:template match="/WTT">
    <root>
        <xsl:copy-of select="start | end | Msg[preceding-sibling::start[1]/@id = following-sibling::end[1]/@id]"/>
    </root>
</xsl:template>

</xsl:stylesheet>

when applied to your XML input, will return:

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <start id="1"/>
   <Msg UserText="Iswritable = true"/>
   <Msg UserText="WriteBuffers = 2"/>
   <Msg UserText="ReadBuffers = 1"/>
   <end id="1"/>
   <start id="2"/>
   <Msg UserText="vertexbuffers = 1"/>
   <end id="2"/>
</root>