Each node is an object of optNode class. Each block is an object of optBlock class. They support the Iterator interface by default, so you can get their children with a normal foreach loop:

foreach($block as $node)
{
	// Your code here
}

See the reference for these two classes in order to find useful methods that help in the tree processing. Write your own code instead of calling defaultTreeProcess() method in your instruction processor. Use the loops and the methods to receive the information about the tags, and then generate some PHP code for them.