Newbie question - dynamic filter on attribute values

I apologize if this has already been discussed, but I am new to XML and XSLT
and have been reading some of the posts and haven't seem to come across my
situation.  I have data similar to the following:

<book attr="1">
    <title attr="10">This is the title</title>
    <chap attr="20">
        <title attr="25">Chapter title 1</title>
        <para attr="26">This is a paragraph in the first chapter</para>
    </chap>        
    <chap attr="20">
        <title attr="25">Chapter title 2</title>
        <para attr="26">This is a paragraph in the second chapter</para>
    </chap>        
</book>

I would like to initially filter out my document based on the attr values.
I will be receiving an array of numbers that correspond to the numbers in
attr.  I only want those elements that match these numbers.  For example, if
I receive 25 and 26, I only want to work with the <title> and <para>
elements.  This array of numbers that I will be receiving will vary from
request to request, meaning I may get a request for only 10 and 25, or just
26.  I would like to somehow dynamically combine this logic into the
following stylesheet, but I am not sure how to do it.

<xsl:template match="chap/title">
    <FormatScope>
	 <Format>
	     <ESC/>TB
		 </Format>
		 <Content>
		     <xsl:apply-templates/>
		 </Content>
		 <Format>
		     <ESC/>TE
		 </Format>
    </FormatScope>
</xsl:template>

<xsl:template match="para">
    <FormatScope>
        <Format>
            <ESC/>PB
        </Format>
        <Content>
            <xsl:apply-templates/>
        </Content>
        <Format>
            <ESC/>PE
        </Format>
    </FormatScope>
</xsl:template>
  
The resulting XML would be:

<FormatScope>
    <Format>
        <ESC/>TB
    </Format>
    <Content>Chapter title 1</Content>
    <Format>
        <ESC/>TE
    </Format>
</FormatScope>

<FormatScope>
    <Format>
        <ESC/>PB
    </Format>
    <Content>This is a paragraph in the first chapter</Content>
    <Format>
        <ESC/>PE
    </Format>
</FormatScope>

<FormatScope>
    <Format>
        <ESC/>TB
    </Format>
    <Content>Chapter title 2</Content>
    <Format>
        <ESC/>TE
    </Format>
</FormatScope>

<FormatScope>
    <Format>
        <ESC/>PB
    </Format>
    <Content>This is a paragraph in the second chapter</Content>
    <Format>
        <ESC/>PE
    </Format>
</FormatScope>


Using XSLT, is there a way to do what I am trying to accomplish?  Any
suggestions are greatly appreciated.

Thanks,
Karen


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