best way to replace placeholder with value in xml string

[PeldOnelymn]

I have replacement xml that has placeholder and its value. I have XML string where I need to search for placeholder and replace that with the value. for example,Placeholder XML:\[code\]<PlaceHolders> <PlaceHolder placeholder="PD1" value="http://stackoverflow.com/questions/11474134/value1" /></PlaceHolders>\[/code\]XML \[code\]<customers> <customer avatarURL="PD1"/></customers>\[/code\]What is the best way to replace "PD1" with value "value1"?