XSLT 1.0 Loop Over Data Array -

i've been plugging away @ xslt stuff , i'm struggling it. i'm using software creates xslt template , adds order object. i've looped on , well, have serialized object need loop over. i've got custom php function processing this, have control on output looks like, don't know how loop on variable.

this have far , i've tried several other combinations:

    <xsl:variable name="mi">         <xsl:value-of select="php:functionstring('client\marketing\helper\order::unserializemarketingitems', increment_id)"/>     </xsl:variable>      <xsl:for-each select="$mi">         <xsl:value-of select="item_id" />      </xsl:for-each> 

because calling custom php function (unserializemarketingdata) can , have tried making xml structure , returned regular object.

but can't seem make happen have loop on object for-each. causes script go white or doesn't output @ all.

so summarize, how can take string of type of data , loop on in xslt template? or right approach?