Working within Repeating Sections
Use the xxf:repeat-position() function to get a reference to the current repeating section. Once the reference is obtained you can then access any field within that repeating section.
Example, set the value of a field on the form based on what is selected within a field of the repeating section
<xf:action ev:event="xforms-value-changed">
<xf:setvalue ref="//CHANGEMGMT_SUMMARY_TARGET_DATE" value="xs:date(//CHANGEMGMT_SUMMARY_TARGET_DATE_CHANGE_LOG-iteration[xxf:repeat-position()]/CHANGEMGMT_SUMMARY_TARGET_DATE_NEW)"/>
</xf:action>