PHP DOMDocument - InsertBefore multiple times

[biperva]

I am a situation where I'd like to add the same content in several locations in an XML file. FYI - first time tackling DOMDocument. Say the xml looks like\[code\]<rrd> <rra> <cdp_prep> <ds> <value>nan</value> </ds> <ds> <value>nan</value> </ds> <ds> <value>nan</value> <ds> </cdp_prep> <database> ... </database> </rra> <rra> <cdp_prep> <ds> <value>nan</value> <ds> </ds> <value>nan</value> <ds> <ds> <value>nan</value> </ds> </cdp_prep> <database> ... </database> </rra></rrd>\[/code\]If i use something like \[code\]$rrdCDPds = $xRRD->query("/rrd/rra/cdp_prep/ds");\[/code\] then i would get all the \[code\]<ds>\[/code\] elements. In this case i would have a length of 6. However, I'm trying to insertBefore on the second \[code\]<ds>\[/code\] of each \[code\]<cdp_prep>\[/code\] element. My issue is if i query on "/rrd/rra/cdp_prep", how do i target the insertBefore on the 2nd \[code\]<ds>\[/code\] element for every \[code\]<cdp_prep>\[/code\] element?