Slicing top and bottom two lines

Question

I want to remove the first and last two lines from the following XML. I am using the following method to omit just the first top and last line, how can I amend it to remove the top two and last two lines? So, to remove node1 and node2.

<node1>
 <node2>
  <context>
    <FirstName>barb</FirstName>
    <LastName>tor</LastName>
  </context>
 </node2>
</node1>

var xml ='<node1><node2><context><FirstName>David</FirstName><LastName>Test</LastName></context></node2></node1>';

const innerStart = xml.indexOf(">") + 1;
const innerEnd   = xml.lastIndexOf("<");
const inner      = xml.slice(innerStart, innerEnd);

console.log(inner)