Set instanceName to selected label of select widget

I have build a form for collecting species in nature conservation with odk Build and downloaded the XML File.
Now I want to change the instanceName to the name of a selected species.
this works, but only with the selected value, not with the selected label by adding the following line:

<bind nodeset="/data/meta/instanceName"  calculate="concat('XY ',/data/art)" type="string" />

Here is my select control:

<select1 appearance="autocomplete"  ref="/data/art">
  <label ref="jr:itext('/data/art:label')"/>
    <label ref="jr:itext('/data/art:option0')"/>
    <label ref="jr:itext('/data/art:option1')"/>

What is the correct syntax to get the label, not the value?
I have tested this and other variants, always without success

<bind nodeset="/data/meta/instanceName"  calculate="concat('XY ',/data/art:label)"  type="string"/>

Thanks a lot for any help!