Problem with Output special char in HTML attribute

Hi at all,
i've a problem with outputting special chars with xsl, particularly
given the following :

<a href="#" tabindex="<?=$tabindex++?>">

rather i want to generate all my link tags with dynamic tabindex
attribute. In xsl i have

<xsl:stylesheet ........
<xsl:output method="html"/>
......
......
<a href=#" tabindex="&#60;?$tabindex++?&#62;">......</a>
.....
.....
</xsl:stylesheet>

but the output produced is :

<a href=#" tabindex="&lt;?$tabindex++?&gt;">....</a>

that is not good because HTML page produced can't be execute
served-side while all php-let are printed in HTML page.
I tried in this way too:

<a href=#">
<xsl:attribute name="tabindex">
    <xsl:text disable-output-escaping="yes">&lt;?$tabindex++?&gt;</xsl:text>
</xsl:attribute>
</a>

but i obtain same result. Note that if i put 
    <xsl:text disable-output-escaping="yes">&lt;?$tabindex++?&gt;</xsl:text>
on xsl not inside attribute, i get correct result. I think problem
concerne special chars inside attribute, problably there must be a
method that i dont'know to put correctly special chars in attribute
value.

Please help me, i'm in trouble.
ANy kind of help is granted.
regards,
Mulp.