Increase number in text string for each match - xslt

Question

I am looking to shorten my XSLT codebase by seeing if XSLT can increase a text number for each match. The text number exists in both the attribute value "label-period0" and the "xls:value-of" value.
The code works, no errors so this is more a question of how to shorten the code and make use of some sort of iteration on a specific character in a string.
I added 2 similar code structures for "period0" and "period1" to better see what exactly are the needed changes in terms of the digit in the text strings.
Source XML file:
<data>
<periods>
<period0><from>2016-01-01</from><to>2016-12-01</to></period0>
<period1><from>2015-01-01</from><to>2015-12-01</to></period1>
<period2><from>2014-01-01</from><to>2014-12-01</to></period2>
<period3><from>2013-01-01</from><to>2013-12-01</to></period3>
</periods>
<balances>
<balance0><instant>2016-12-31</instant></balance0>
<balance1><instant>2015-12-31</instant></balance1>
<balance2><instant>2014-12-31</instant></balance2>
<balance3><instant>2013-12-31</instant></balance3>
</balances>
</data>
XSL file:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:transform
version="3.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>
<xsl:output method="xml" indent="yes"/>
<!-- Block all data that has no user defined template -->
<xsl:mode on-no-match="shallow-skip"/>
<xsl:template match="data">
<results>
<periods>
<periods label="period0">
<xsl:value-of
select =
"concat(periods/period0/from, '--', periods/period0/to)"
/>
</periods>
<periods label="period1">
<xsl:value-of
select =
"concat(periods/period1/from, '--', periods/period1/to)"
/>
</periods>
<!-- Etc for period [2 and 3]-->
</periods>
<balances>
<balance label="balance0">
<xsl:value-of select ="balances/balance0/instant"/>
</balance>
<!-- Etc for balance [1,2 and 3] -->
</balances>
</results>
</xsl:template>
</xsl:transform>
Result:
<?xml version="1.0" encoding="UTF-8"?>
<results>
<periods>
<periods label="period0">2016-01-01--2016-12-01</periods>
<periods label="period1">2015-01-01--2015-12-01</periods>
</periods>
<balances>
<balance label="balance0">2016-12-31</balance>
</balances>
</results>
Wanted result:
(with an XSL that steps the digit in the text string, or any other logics in XSL that could cater for manipulating the digit in text string)
<?xml version="1.0" encoding="UTF-8"?>
<results>
<periods>
<periods label="period0">2016-01-01--2016-12-01</periods>
<periods label="period1">2015-01-01--2015-12-01</periods>
<periods label="period2">2014-01-01--2015-12-01</periods>
<periods label="period3">2013-01-01--2015-12-01</periods>
</periods>
<balances>
<balance label="balance0">2016-12-31</balance>
<balance label="balance1">2015-12-31</balance>
<balance label="balance2">2014-12-31</balance>
<balance label="balance3">2013-12-31</balance>
</balances>
</results>

Answer 1

Couldn't you do simply something like:
<xsl:template match="/data">
<results>
<periods>
<xsl:for-each select="periods/*">
<periods label="{name()}">
<xsl:value-of select="from"/>
<xsl:text>--</xsl:text>
<xsl:value-of select="to"/>
</periods>
</xsl:for-each>
</periods>
<balances>
<xsl:for-each select="balances/*">
<balance label="{name()}">
<xsl:value-of select="instant"/>
</balance>
</xsl:for-each>
</balances>
</results>
</xsl:template>
If you want to do your own numbering, you can change:
<periods label="{name()}">
to:
<periods label="period{position() - 1}">