Need help putting things in the right place

parser.php

<?php
require_once 'util.php';

class parser {
	public $instructions = array(); // Array 	- Instructions for the interpreter
	public $css; 					// String 	- The formatted css code
	public $tree = array();			// Array 	- The output tree
	public $lines = array();		// Array 	- Lines of the formatted css code
	public $level = array();		// Array 	- List of different arrays to append to
	public $nest = 0;				// Int 		- How far nested are we?

	public function tokenize() {
		$in = $this->instructions;
		$lines = $this->lines;

		foreach ($lines as $line) {
			$parts = explode(" ", $line);

			$ending = $parts[count($parts) - 1];

			switch ($ending) {
				case '{':
					$in[] = array('opcode' => 'OPEN_BRACE', 'args' => $parts);
					break;
				case '}':
					$in[] = array('opcode' => 'CLOSE_BRACE', 'args' => $parts);
					break;
				case "\n":
					$in[] = array('opcode' => 'END_LINE', 'args' => $parts);
					break;
				default:
					$in[] = array('opcode' => 'OTHER', 'args' => $parts);
					break;
			}
		}

		$this->instructions = $in;
	}

	public function interpret() {
		$name = '';
		foreach ($this->instructions as $index => $in) {
			$code = $in['opcode'];
			$args = $in['args'];

			switch($code) {
				case 'OPEN_BRACE':
					$this->nest++;
					$name = $args;
					array_pop($name);
					array_map('trim', $name);
					$name = implode(' ', $name);
					$this->level[] = array();
					break;
				case 'CLOSE_BRACE':
					$this->nest--;
					$this->tree[$name] = $this->level[-1];
					array_pop($this->level);
					break;
				
				default:
					$this->level[-1][] = $args;
					break;
			}
		}
	}

	public function parse($css) {
		$this->css = Util::normalise($css, false);
		$this->lines = explode("\n", $this->css);
		$this->lines = array_map("trim", $this->lines);
		$this->lines = array_filter($this->lines);
		
		$this->tokenize();	
		$this->interpret();

		print_r($this->tree);
	}
}

$parser = new parser();
$parser->parse(file_get_contents('css.css'));