best way to replace placeholder with value in xml string
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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**:

    <PlaceHolders>
      <PlaceHolder placeholder="PD1" value="value1" />
    </PlaceHolders>

**XML** 

    <customers>
      <customer avatarURL="PD1"/>
    </customers>

What is the best way to replace "PD1" with value "value1"?