Increment Letter's in XSL 1.0 - xslt

Question

I have from XML for example the String "AA"
and i need to increment it Like:
AA AB AC AD AE (...) AZ BA BB (...)
For example increment it for 35 times (coming from a varaible called (`xsl:variable name ="NumIncr">)) starting at AA and finishing in BG.
The string don't always have "AA" can be any 2 letters...
Any idea to do this?!
I think the <xsl:number> tag can help, but still the problem to pass from letters to numbers.
Need something like
<fo:table-cell border-collapse="collapse" border-color="gray" font-family="Helvetica" font-size="8pt" border="solid 1pt gray" padding="1pt" display-align="before">
<fo:block text-align="center">
<xsl:value-of select="string($Sequence)"/>
</fo:block>
</fo:table-cell>
Where $sequence is the AA AB AC (...)
Can writte evrything in the same cell, the problem isn't the output but the tamplate to increment the AA
HELP!!!

Answer 1

To translate a string like "AA" to its numerical value, you can use the following template:
<xsl:template name="string-to-num">
<xsl:param name="string"/>
<xsl:param name="alpha" select="'ABCDEFGHIJKLMNOPQRSTUVWXYZ'"/>
<xsl:param name="magnitude" select="1"/>
<xsl:param name="carryover" select="0"/>
<xsl:param name="bit" select="substring($string, string-length($string), 1)"/>
<xsl:param name="bit-value" select="string-length(substring-before($alpha, $bit)) + 1"/>
<xsl:variable name="return" select="$carryover + $bit-value * $magnitude"/>
<xsl:choose>
<xsl:when test="string-length($string) > 1">
<xsl:call-template name="string-to-num">
<xsl:with-param name="string" select="substring($string, 1, string-length($string) - 1)"/>
<xsl:with-param name="magnitude" select="string-length($alpha) * $magnitude"/>
<xsl:with-param name="carryover" select="$return"/>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$return" />
</xsl:otherwise>
</xsl:choose>
</xsl:template>
Some examples of calling the template:
<xsl:call-template name="string-to-num">
<xsl:with-param name="string">A</xsl:with-param>
</xsl:call-template>
returns 1;
<xsl:call-template name="string-to-num">
<xsl:with-param name="string">Z</xsl:with-param>
</xsl:call-template>
returns 26;
<xsl:call-template name="string-to-num">
<xsl:with-param name="string">AA</xsl:with-param>
</xsl:call-template>
returns 27;
<xsl:call-template name="string-to-num">
<xsl:with-param name="string">ZZ</xsl:with-param>
</xsl:call-template>
returns 702;
<xsl:call-template name="string-to-num">
<xsl:with-param name="string">AAA</xsl:with-param>
</xsl:call-template>
returns 703.
These results are the exact reverse of:
<xsl:number value="$return" format="A"/>