diff --git a/app/Cfnpp/Compiler.php b/app/Cfnpp/Compiler.php
index 2c302f1..2e680eb 100644
--- a/app/Cfnpp/Compiler.php
+++ b/app/Cfnpp/Compiler.php
@@ -44,7 +44,7 @@ class Compiler implements \App\Engine\ICompile
 	/**
 	 * Stores current state of the document so it can be mutated mid-pass.
 	 *
-	 * @var Document
+	 * @var ?Document
 	 */
 	protected $document;
 
@@ -73,6 +73,15 @@ class Compiler implements \App\Engine\ICompile
 		$this->merge_functions[$name] = $callback;
 	}
 
+	/**
+	 * Add a condition to the document currently being processed.
+	 *
+	 * The only appropriate place to call this is from the document functions
+	 *
+	 * @param  string $name name of condition to create
+	 * @param  Node   $node
+	 * @return void
+	 */
 	public function addCondition(string $name, Node $node): void
 	{
 		$conditions = $this->document->getChildByName('Conditions');
@@ -109,12 +118,11 @@ class Compiler implements \App\Engine\ICompile
 		$cfnpp_functions = new Functions($this, $options);
 		$cfnpp_functions->register($this);
 
-		$this->document = $this->pass_0($documents, $options);
-		$this->pass_1($this->document, $options);
-		$this->pass_2($this->document, $options);
+		$this->document = $document = $this->pass_0($documents, $options);
+		$this->pass_1($document, $options);
+		$this->pass_2($document, $options);
 
 		return $this->document;
-
 		// Process each passed document
 		/*
 		foreach ($documents as $next_document)
@@ -294,13 +302,14 @@ class Compiler implements \App\Engine\ICompile
 			{
 				$variables[] = $node->getValue();
 			}
+			/*
+			// TODO: Reimplement
 			elseif ($node instanceof NodeFunctionValue &&
 				$node->getName() == 'expr')
 			{
-				$parser = new \App\Cfnpp\Expression\Parser();
-				$expression = $parser->parse($node->getValue());
+				$expression = new \App\Cfnpp\Expression\Expression($node->getValue());
 				$variables = array_merge($variables, $expression->getReferencedVariables());
-			}
+			}*/
 		}
 
 		return $variables;
diff --git a/app/Cfnpp/Expression/Expression.php b/app/Cfnpp/Expression/Expression.php
index b0c4d97..1cb9791 100644
--- a/app/Cfnpp/Expression/Expression.php
+++ b/app/Cfnpp/Expression/Expression.php
@@ -7,8 +7,18 @@ namespace App\Cfnpp\Expression;
 use App\Util\GraphNode;
 use App\Util\Stack;
 
+/**
+ * Represents an expression and handles tokenizing, parsing, and executing
+ * expressions.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Expression
 {
+	/**
+	 * References to all Token implementations this class can handle.
+	 * @var string[]
+	 */
 	public const TOKEN_TYPES = [
 		Token\NumericLiteral::class,
 		Token\OperatorUnary::class,
@@ -17,10 +27,26 @@ class Expression
 		Token\Variable::class
 	];
 
+	/**
+	 * Solved expression this represents.
+	 * @var GraphNode[]
+	 */
 	protected $nodes;
 
-	protected $solved = false;
+	/**
+	 * Referencing to our compilation state for accessing variables/parameters.
+	 * @var \App\Engine\IOptions
+	 */
+	protected $options;
 
+	/**
+	 * Create a new expression.
+	 *
+	 * Expression is tokenized, parsed, and solved on creation.
+	 *
+	 * @param string               $expression
+	 * @param \App\Engine\IOptions $options
+	 */
 	public function __construct(string $expression, \App\Engine\IOptions $options)
 	{
 		$tokens = static::tokenize($expression);
@@ -29,7 +55,16 @@ class Expression
 		$this->options = $options;
 	}
 
-	public function isComplete()
+	/**
+	 * Check whether this expression is 'complete'.
+	 *
+	 * Complete is defined as having been solved down to a single value, or array
+	 * of single values none of which are still tokens. That is, we have a set of
+	 * computed scalars and no unresolved var/param references.
+	 *
+	 * @return bool
+	 */
+	public function isComplete(): bool
 	{
 		// I think this works? If we resolved down to a flat set of values and
 		// all are scalar, then we're done?
@@ -49,26 +84,55 @@ class Expression
 		return $complete;
 	}
 
-	public function count()
+	/**
+	 * Check how many values are contained in the solution.
+	 *
+	 * @return int
+	 */
+	public function count(): int
 	{
 		return sizeof($this->nodes);
 	}
 
+	/**
+	 * Assuming the solution contains only a single value, fetch it.
+	 *
+	 * @return mixed
+	 */
 	public function getValue()
 	{
 		return $this->nodes[0]->getValue();
 	}
 
+	/**
+	 * Fetch the solution as an array.
+	 *
+	 * Only valid if the solution is complete
+	 *
+	 * @return mixed[]
+	 */
 	public function toArray(): array
 	{
 		return static::unwrap($this->nodes);
 	}
 
+	/**
+	 * Convert an incomplete solution into a CloudFormation condition using
+	 * CloudFormation intrinsic functions.
+	 *
+	 * @return mixed[]
+	 */
 	public function toCloudformation(): array
 	{
 		return static::cloudformation($this->nodes);
 	}
 
+	/**
+	 * Convert an expression string into a series of tokens.
+	 *
+	 * @param  string  $expression
+	 * @return Token[]
+	 */
 	protected static function tokenize(string $expression): array
 	{
 		$tokens = [];
@@ -95,6 +159,12 @@ class Expression
 		return $tokens;
 	}
 
+	/**
+	 * Build a tree out of a series of tokens.
+	 *
+	 * @param  Token[]     $tokens
+	 * @return GraphNode[]
+	 */
 	protected static function parse(array $tokens): array
 	{
 		$stack = new Stack();
@@ -115,6 +185,7 @@ class Expression
 			{
 				$node = new GraphNode($token);
 				$node->appendChild($stack->pop());
+				// @phan-suppress-next-line PhanPluginDuplicateAdjacentStatement
 				$node->appendChild($stack->pop());
 				$stack->push($node);
 			}
@@ -122,6 +193,15 @@ class Expression
 		return $stack->get();
 	}
 
+	/**
+	 * Solve a tree of tokens by inserting all variable values and wherever possible
+	 * resolving all functions.
+	 *
+	 * @param  GraphNode[]         $nodes      parsed tree
+	 * @param  array<string,mixed> $variables  variable names and values
+	 * @param  string[]            $parameters parameter names
+	 * @return GraphNode[]
+	 */
 	protected static function solve(array $nodes, array $variables = [], array $parameters = []): array
 	{
 		$root = new GraphNode();
@@ -129,21 +209,24 @@ class Expression
 		{
 			$root->appendChild($node);
 		}
-		$nodes = static::fillVariables($root->getChildren(), $variables, $parameters);
-		$nodes = static::collapse($root->getChildren());
+		static::fillVariables($root->getChildren(), $variables, $parameters);
+		static::collapse($root->getChildren());
 		return $root->getChildren();
 	}
 
-	protected static function execute(array $nodes, array $variables = [], array $parameters = [])
-	{
-		return static::unwrap(static::solve($nodes, $variables, $parameters));
-	}
-
+	/**
+	 * Convert a tree of of nodes into something that could be a valid CloudFormation
+	 * condition.
+	 *
+	 * @param  GraphNode[] $nodes
+	 * @throws \Exception  if the remaining nodes contain functions that cannot be expressed in cloudformation
+	 * @return mixed[]
+	 */
 	protected static function cloudformation(array $nodes): array
 	{
 		foreach ($nodes as $node)
 		{
-			$node->walk(static function($node) {
+			$node->walk(static function(GraphNode $node): void {
 				if (is_scalar($node->getValue()))
 				{
 					return;
@@ -164,11 +247,20 @@ class Expression
 		return $nodes[0]->getValue();
 	}
 
+	/**
+	 * Fill all variable values by replacing variable tokens with their actual values.
+	 *
+	 * @param  GraphNode[]         $nodes
+	 * @param  array<string,mixed> $variables  variable values
+	 * @param  string[]            $parameters parameter names
+	 * @throws \Exception          if a reference is made to an undefined variable
+	 * @return void
+	 */
 	protected static function fillVariables(array $nodes, array $variables, array $parameters): void
 	{
 		foreach ($nodes as $node)
 		{
-			$node->walk(static function($node) use ($variables, $parameters) {
+			$node->walk(static function(GraphNode $node) use ($variables, $parameters): void {
 				if ($node->getValue() instanceof Token\Variable)
 				{
 					$var_name = $node->getValue()->getName();
@@ -189,11 +281,17 @@ class Expression
 		}
 	}
 
+	/**
+	 * 'collapse' a node tree by executing nodes.
+	 *
+	 * @param  GraphNode[] $nodes
+	 * @return void
+	 */
 	protected static function collapse(array $nodes): void
 	{
 		foreach ($nodes as $node)
 		{
-			$node->walk(static function($node) {
+			$node->walk(static function(GraphNode $node): void {
 				if ($node->getValue() instanceof Token\Parameter)
 				{
 					return;
@@ -221,9 +319,18 @@ class Expression
 		}
 	}
 
+	/**
+	 * Unwrap an array of nodes by returning their values.
+	 *
+	 * Not valid if any nodes still contain children, as the assumption is that
+	 * those nodes are unresolved.
+	 *
+	 * @param  GraphNode[] $nodes
+	 * @return mixed[]
+	 */
 	protected static function unwrap(array $nodes)
 	{
-		return array_map(static function($node) {
+		return array_map(/** @return mixed */ static function(GraphNode $node) {
 			if ($node->hasChildren())
 			{
 				throw new \Exception('Cannot unwrap node: still has children');
diff --git a/app/Cfnpp/Expression/ICloudformationNative.php b/app/Cfnpp/Expression/ICloudformationNative.php
index 6b3dae1..338d907 100644
--- a/app/Cfnpp/Expression/ICloudformationNative.php
+++ b/app/Cfnpp/Expression/ICloudformationNative.php
@@ -4,7 +4,19 @@ declare(strict_types=1);
 
 namespace App\Cfnpp\Expression;
 
+/**
+ * Token type that supports being converted directly to a CloudFormation intrinsic.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 interface ICloudformationNative
 {
+	/**
+	 * Convert this token to a CloudFormation intrinsic, formatted as a simple
+	 * PHP array.
+	 *
+	 * @param  ?\App\Util\GraphNode[] $arguments requested token parameters
+	 * @return mixed[]
+	 */
 	public function toCloudformation(?array $arguments = null): array;
 }
diff --git a/app/Cfnpp/Expression/Token.php b/app/Cfnpp/Expression/Token.php
index 9bb13af..8164f08 100644
--- a/app/Cfnpp/Expression/Token.php
+++ b/app/Cfnpp/Expression/Token.php
@@ -5,13 +5,36 @@ declare(strict_types=1);
 namespace App\Cfnpp\Expression;
 
 /**
- * Token parent class.
+ * Token parsed out of an expression.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
  */
 abstract class Token
 {
+	/**
+	 * Determine whether the passed stream contains an instance of this token.
+	 *
+	 * @param  string $stream
+	 * @return bool
+	 */
 	abstract public static function isToken(string $stream): bool;
 
+	/**
+	 * Consume a token from the passed stream.
+	 *
+	 * This method is expected to modify the stream to remove all
+	 * consumed characters
+	 *
+	 * @param  string $stream
+	 * @return Token
+	 */
 	abstract public static function getToken(string &$stream): Token;
 
+	/**
+	 * Execute the token given the requested parameters.
+	 *
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	abstract public function execute(?array $arguments = null);
 }
diff --git a/app/Cfnpp/Expression/Token/NumericLiteral.php b/app/Cfnpp/Expression/Token/NumericLiteral.php
index d1bf00c..e27885c 100644
--- a/app/Cfnpp/Expression/Token/NumericLiteral.php
+++ b/app/Cfnpp/Expression/Token/NumericLiteral.php
@@ -7,15 +7,34 @@ namespace App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenLiteral;
 
+/**
+ * A number literal.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class NumericLiteral extends TokenLiteral
 {
+	/**
+	 * Value of this literal.
+	 * @var int|float
+	 */
 	protected $value;
 
+	/**
+	 * New number literal.
+	 *
+	 * @param int|float $value
+	 */
 	public function __construct($value)
 	{
 		$this->value = $value;
 	}
 
+	/**
+	 * Get the value of this literal.
+	 *
+	 * @return int|float
+	 */
 	public function getValue()
 	{
 		return $this->value;
@@ -55,6 +74,12 @@ class NumericLiteral extends TokenLiteral
 		return new NumericLiteral($buffer);
 	}
 
+	/**
+	 * Get the value of this token.
+	 *
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		return $this->getValue();
diff --git a/app/Cfnpp/Expression/Token/OperatorBinary.php b/app/Cfnpp/Expression/Token/OperatorBinary.php
index 3715f2f..3510438 100644
--- a/app/Cfnpp/Expression/Token/OperatorBinary.php
+++ b/app/Cfnpp/Expression/Token/OperatorBinary.php
@@ -8,22 +8,45 @@ use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenBinary;
 use App\Cfnpp\Expression\ICloudformationNative;
 
+/**
+ * Basic comparison operators that take two parameters.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class OperatorBinary extends TokenBinary implements ICloudformationNative
 {
+	/**
+	 * List of valid operators.
+	 * @var string[]
+	 */
 	public const OPERATORS = [
 		'and',
 		'or',
 		'eq'
 	];
 
+	/**
+	 * The operator this instance represents.
+	 * @var string
+	 */
 	protected $operator;
 
-	public function __construct($operator)
+	/**
+	 * New binary operator.
+	 *
+	 * @param string $operator
+	 */
+	public function __construct(string $operator)
 	{
 		$this->operator = $operator;
 	}
 
-	public function getOperator()
+	/**
+	 * Get the operator this instance represents.
+	 *
+	 * @return string
+	 */
+	public function getOperator(): string
 	{
 		return $this->operator;
 	}
@@ -56,6 +79,15 @@ class OperatorBinary extends TokenBinary implements ICloudformationNative
 		throw new \Exception('Could not parse OperatorBinary');
 	}
 
+	/**
+	 * Execute the operator.
+	 *
+	 * Suppressing accesses to arguments since this is guaranteed valid
+	 * unless there are bugs in Expression.
+	 * @suppress PhanTypeArraySuspiciousNullable
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		$value1 = $arguments[0]->getValue();
@@ -80,11 +112,9 @@ class OperatorBinary extends TokenBinary implements ICloudformationNative
 				{
 					return $value1;
 				}
-				else
-				{
+
 					return null;
-				}
-				// no break
+
 			case 'or':
 				if (is_scalar($value1) && is_scalar($value2))
 				{
@@ -102,11 +132,9 @@ class OperatorBinary extends TokenBinary implements ICloudformationNative
 				{
 					return $value1;
 				}
-				else
-				{
+
 					return null;
-				}
-				// no break
+
 			case 'eq':
 				if (is_scalar($value1) && is_scalar($value2))
 				{
@@ -116,16 +144,23 @@ class OperatorBinary extends TokenBinary implements ICloudformationNative
 				{
 					return true;
 				}
-				else
-				{
+
 					return null;
-				}
-				// no break
+
 			default:
 				throw new \Exception('Missing implementation for unary operator: '.$this->getOperator());
 		}
 	}
 
+	/**
+	 * Convert this token into a CloudFormation intrinsic.
+	 *
+	 * Suppressing accesses to arguments since this is guaranteed valid
+	 * unless there are bugs in Expression.
+	 * @suppress PhanTypeArraySuspiciousNullable
+	 * @param  ?\App\Util\GraphNode[] $arguments
+	 * @return mixed[]
+	 */
 	public function toCloudformation(?array $arguments = null): array
 	{
 		$value1 = $arguments[0]->getValue();
diff --git a/app/Cfnpp/Expression/Token/OperatorUnary.php b/app/Cfnpp/Expression/Token/OperatorUnary.php
index 6fbc4a0..02acc1b 100644
--- a/app/Cfnpp/Expression/Token/OperatorUnary.php
+++ b/app/Cfnpp/Expression/Token/OperatorUnary.php
@@ -8,19 +8,42 @@ use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenUnary;
 use App\Cfnpp\Expression\ICloudformationNative;
 
+/**
+ * Basic operators that take one parameter.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class OperatorUnary extends TokenUnary implements ICloudformationNative
 {
+	/**
+	 * List of valid operators.
+	 * @var string[]
+	 */
 	public const OPERATORS = [
 		'not'
 	];
 
+	/**
+	 * The operator this instance represents.
+	 * @var string
+	 */
 	protected $operator;
 
+	/**
+	 * New unary operator.
+	 *
+	 * @param string $operator
+	 */
 	public function __construct($operator)
 	{
 		$this->operator = $operator;
 	}
 
+	/**
+	 * Get the operator this instance represents.
+	 *
+	 * @return string
+	 */
 	public function getOperator()
 	{
 		return $this->operator;
@@ -54,6 +77,15 @@ class OperatorUnary extends TokenUnary implements ICloudformationNative
 		throw new \Exception('Could not parse OperatorUnary');
 	}
 
+	/**
+	 * Execute the operator.
+	 *
+	 * Suppressing accesses to arguments since this is guaranteed valid
+	 * unless there are bugs in Expression.
+	 * @suppress PhanTypeArraySuspiciousNullable
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		$value = $arguments[0]->getValue();
@@ -66,6 +98,15 @@ class OperatorUnary extends TokenUnary implements ICloudformationNative
 		}
 	}
 
+	/**
+	 * Convert this token into a CloudFormation intrinsic.
+	 *
+	 * Suppressing accesses to arguments since this is guaranteed valid
+	 * unless there are bugs in Expression.
+	 * @suppress PhanTypeArraySuspiciousNullable
+	 * @param  ?\App\Util\GraphNode[] $arguments
+	 * @return mixed[]
+	 */
 	public function toCloudformation(?array $arguments = null): array
 	{
 		$value = $arguments[0]->getValue();
diff --git a/app/Cfnpp/Expression/Token/Parameter.php b/app/Cfnpp/Expression/Token/Parameter.php
index cd1b4be..cbbe37b 100644
--- a/app/Cfnpp/Expression/Token/Parameter.php
+++ b/app/Cfnpp/Expression/Token/Parameter.php
@@ -8,16 +8,35 @@ use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenLiteral;
 use App\Cfnpp\Expression\ICloudformationNative;
 
+/**
+ * Represents a reference to a CloudFormation parameter.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Parameter extends TokenLiteral implements ICloudformationNative
 {
+	/**
+	 * Name of the referenced parameter.
+	 * @var string
+	 */
 	protected $name;
 
-	public function __construct($name)
+	/**
+	 * New parameter.
+	 * @string $name
+	 * @param string $name
+	 */
+	public function __construct(string $name)
 	{
 		$this->name = $name;
 	}
 
-	public function getName()
+	/**
+	 * Get the name of the parameter.
+	 *
+	 * @return string
+	 */
+	public function getName(): string
 	{
 		return $this->name;
 	}
@@ -48,11 +67,23 @@ class Parameter extends TokenLiteral implements ICloudformationNative
 		return new Parameter($buffer);
 	}
 
+	/**
+	 * Get the value of this token.
+	 *
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		throw new \Exception('Unreplaced parameter');
 	}
 
+	/**
+	 * Return the cloudformation representation of a reference to a parameter.
+	 *
+	 * @param  ?\App\Util\GraphNode[] $arguments
+	 * @return mixed[]
+	 */
 	public function toCloudformation(?array $arguments = null): array
 	{
 		return ['Ref' => $this->getName()];
diff --git a/app/Cfnpp/Expression/Token/StringLiteral.php b/app/Cfnpp/Expression/Token/StringLiteral.php
index 9114e3d..7288831 100644
--- a/app/Cfnpp/Expression/Token/StringLiteral.php
+++ b/app/Cfnpp/Expression/Token/StringLiteral.php
@@ -7,16 +7,35 @@ namespace App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenLiteral;
 
+/**
+ * A string literal.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class StringLiteral extends TokenLiteral
 {
+	/**
+	 * Value of the string literal.
+	 * @var string
+	 */
 	protected $value;
 
-	public function __construct($value)
+	/**
+	 * New string literal.
+	 *
+	 * @param string $value
+	 */
+	public function __construct(string $value)
 	{
 		$this->value = $value;
 	}
 
-	public function getValue()
+	/**
+	 * Get the value of this literal.
+	 *
+	 * @return string
+	 */
+	public function getValue(): string
 	{
 		return $this->value;
 	}
@@ -63,6 +82,12 @@ class StringLiteral extends TokenLiteral
 		return new StringLiteral($buffer);
 	}
 
+	/**
+	 * Get the value of this token.
+	 *
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		return $this->getValue();
diff --git a/app/Cfnpp/Expression/Token/Variable.php b/app/Cfnpp/Expression/Token/Variable.php
index edb2b06..a1c94df 100644
--- a/app/Cfnpp/Expression/Token/Variable.php
+++ b/app/Cfnpp/Expression/Token/Variable.php
@@ -7,16 +7,35 @@ namespace App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\Token;
 use App\Cfnpp\Expression\TokenLiteral;
 
+/**
+ * Reference to a variable.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Variable extends TokenLiteral
 {
+	/**
+	 * Name of the variable.
+	 * @var string
+	 */
 	protected $name;
 
-	public function __construct($name)
+	/**
+	 * New variable reference.
+	 *
+	 * @param string $name
+	 */
+	public function __construct(string $name)
 	{
 		$this->name = $name;
 	}
 
-	public function getName()
+	/**
+	 * Get the name of the variable.
+	 *
+	 * @return string
+	 */
+	public function getName(): string
 	{
 		return $this->name;
 	}
@@ -47,6 +66,13 @@ class Variable extends TokenLiteral
 		return new Variable($buffer);
 	}
 
+	/**
+	 * Not valid. Variable replacement should be handled by the expression parser.
+	 *
+	 * @param  ?\App\Util\GraphNode[]                $arguments
+	 * @throws \Exception                            if called
+	 * @return \App\Util\GraphNode|Token|scalar|null
+	 */
 	public function execute(?array $arguments = null)
 	{
 		throw new \Exception('Unreplaced variable');
diff --git a/app/Cfnpp/Functions.php b/app/Cfnpp/Functions.php
index 79eb493..3ca96e8 100644
--- a/app/Cfnpp/Functions.php
+++ b/app/Cfnpp/Functions.php
@@ -119,6 +119,13 @@ class Functions
 		return new NodeValue(null, $node->hasName() ? $node->getName() : null, $value);
 	}
 
+	/**
+	 * Create a reference to a CloudFormation parameter.
+	 *
+	 * @param  Node         $node
+	 * @param  NodeFunction $function
+	 * @return ?Node
+	 */
 	public function f_param(Node $node, NodeFunction $function): ?Node
 	{
 		if (!($function instanceof NodeFunctionValue))
@@ -201,6 +208,8 @@ class Functions
 	 * @param  NodeFunction $function
 	 * @return ?Node
 	 */
+	/*
+	 * TODO: Reimplement
 	public function f_expr(Node $node, NodeFunction $function): ?Node
 	{
 		if (!($function instanceof NodeFunctionValue))
@@ -217,4 +226,5 @@ class Functions
 
 		return $result;
 	}
+	 */
 }
diff --git a/app/Util/GraphNode.php b/app/Util/GraphNode.php
index e1eb212..1d08e00 100644
--- a/app/Util/GraphNode.php
+++ b/app/Util/GraphNode.php
@@ -4,71 +4,143 @@ declare(strict_types=1);
 
 namespace App\Util;
 
+/**
+ * Represents a node in a tree.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class GraphNode
 {
+	/**
+	 * Parent of this node.
+	 * @var GraphNode
+	 */
 	protected $parent;
 
+	/**
+	 * Value of this node.
+	 * @var mixed
+	 */
 	protected $value;
 
+	/**
+	 * Children of this node.
+	 * @var GraphNode[]
+	 */
 	protected $children;
 
+	/**
+	 * Create a new graph node.
+	 *
+	 * @param mixed $value
+	 */
 	public function __construct($value = null)
 	{
 		$this->value = $value;
 		$this->children = [];
 	}
 
-	public function __invoke()
-	{
-		return $this->value;
-	}
-
+	/**
+	 * Set the value of this node.
+	 *
+	 * @param  mixed $value
+	 * @return void
+	 */
 	public function setValue($value): void
 	{
 		$this->value = $value;
 	}
 
+	/**
+	 * Get the value of this node.
+	 *
+	 * @return mixed
+	 */
 	public function getValue()
 	{
 		return $this->value;
 	}
 
+	/**
+	 * Set the parent node of this node.
+	 *
+	 * @param  GraphNode $node
+	 * @return void
+	 */
 	public function setParent(GraphNode $node): void
 	{
 		$this->parent = $node;
 	}
 
+	/**
+	 * Determine whether this node has a parent.
+	 *
+	 * @return bool
+	 */
 	public function hasParent(): bool
 	{
 		return isset($this->parent);
 	}
 
+	/**
+	 * Get this node's parent node.
+	 *
+	 * @return GraphNode
+	 */
 	public function getParent(): GraphNode
 	{
 		return $this->parent;
 	}
 
+	/**
+	 * Count how many child nodes this node has.
+	 *
+	 * @return int
+	 */
 	public function countChildren(): int
 	{
 		return sizeof($this->children);
 	}
 
+	/**
+	 * Determine whether this node has any children.
+	 *
+	 * @return bool
+	 */
 	public function hasChildren(): bool
 	{
 		return sizeof($this->children) > 0;
 	}
 
+	/**
+	 * Fetch all of this node's children.
+	 *
+	 * @return GraphNode[]
+	 */
 	public function getChildren(): array
 	{
 		return $this->children;
 	}
 
+	/**
+	 * Add a node to this child's list of children.
+	 *
+	 * @param  GraphNode $child
+	 * @return void
+	 */
 	public function appendChild(GraphNode $child): void
 	{
 		$this->children[] = $child;
 		$child->setParent($this);
 	}
 
+	/**
+	 * Replace a child node with another node.
+	 *
+	 * @param  GraphNode $original
+	 * @param  GraphNode $new
+	 * @return void
+	 */
 	public function replaceChild(GraphNode $original, GraphNode $new): void
 	{
 		for ($i = 0; $i < sizeof($this->children); $i++)
@@ -82,11 +154,22 @@ class GraphNode
 		}
 	}
 
+	/**
+	 * Remove all children of this node.
+	 *
+	 * @return void
+	 */
 	public function clearChildren(): void
 	{
 		$this->children = [];
 	}
 
+	/**
+	 * Add a child node by value.
+	 *
+	 * @param  mixed     $value value to add as a child
+	 * @return GraphNode the node created as a child
+	 */
 	public function add($value): GraphNode
 	{
 		$this->children[] = new GraphNode($value);
@@ -94,11 +177,26 @@ class GraphNode
 		return end($this->children);
 	}
 
+	/**
+	 * Walk through this node and all children, calling callback on each node.
+	 *
+	 * Callback is called on a node's children before a node
+	 *
+	 * @param  callable $callback callback(GraphNode $node): void
+	 * @return void
+	 */
 	public function walk(callable $callback)
 	{
 		static::walkNodes([$this], $callback);
 	}
 
+	/**
+	 * Internal function for recursively visiting all nodes.
+	 *
+	 * @param  GraphNode[] $nodes
+	 * @param  callable    $callback
+	 * @return void
+	 */
 	protected static function walkNodes(array $nodes, callable $callback)
 	{
 		foreach ($nodes as $node)
diff --git a/app/Util/Stack.php b/app/Util/Stack.php
index f052a53..49926b9 100644
--- a/app/Util/Stack.php
+++ b/app/Util/Stack.php
@@ -4,25 +4,53 @@ declare(strict_types=1);
 
 namespace App\Util;
 
+/**
+ * Basic stack data structure.
+ *
+ * @author Adam Pippin <hello@adampippin.ca>
+ */
 class Stack
 {
+	/**
+	 * Stack data.
+	 * @var mixed[]
+	 */
 	protected $stack;
 
+	/**
+	 * Create a new stack.
+	 */
 	public function __construct()
 	{
 		$this->stack = [];
 	}
 
+	/**
+	 * Count how many items this stack contains.
+	 *
+	 * @return int
+	 */
 	public function count(): int
 	{
 		return sizeof($this->stack);
 	}
 
+	/**
+	 * Get all items in this stack.
+	 *
+	 * @return mixed[]
+	 */
 	public function get(): array
 	{
 		return $this->stack;
 	}
 
+	/**
+	 * Pop an item off of this stack.
+	 *
+	 * @param  int   $offset offset from the end to pop if not the last element
+	 * @return mixed
+	 */
 	public function pop(int $offset = 0)
 	{
 		if (sizeof($this->stack) < $offset + 1)
@@ -32,6 +60,12 @@ class Stack
 		return array_splice($this->stack, -1 * ($offset + 1), 1)[0];
 	}
 
+	/**
+	 * Push an item onto the end of the stack.
+	 *
+	 * @param  mixed $value
+	 * @return void
+	 */
 	public function push($value): void
 	{
 		array_push($this->stack, $value);