diff --git a/modules/generative_grammar/generator.cpp b/modules/generative_grammar/generator.cpp
index caed0fc05f..f1a81b38ef 100644
--- a/modules/generative_grammar/generator.cpp
+++ b/modules/generative_grammar/generator.cpp
@@ -4,7 +4,7 @@
 #include "macros.h"
 
 void Generator::_bind_methods() {
-	BIND_HPROPERTY(Variant::OBJECT, state, PROPERTY_HINT_RESOURCE_TYPE, "Symbol");
+	BIND_HPROPERTY(Variant::OBJECT, state, PROPERTY_HINT_RESOURCE_TYPE, "Sentence");
 }
 
 void Generator::ready() {
@@ -19,6 +19,13 @@ void Generator::_notification(int what) {
 			return;
 		case NOTIFICATION_READY:
 			ready();
+		case NOTIFICATION_CHILD_ORDER_CHANGED:
+			for (Variant child : get_children()) {
+				if (Rule * rule{ cast_to<Rule>(child) }) {
+					this->rule = rule;
+					return;
+				}
+			}
 			return;
 	}
 }
diff --git a/modules/generative_grammar/generator.h b/modules/generative_grammar/generator.h
index e0bca38510..513fc469e1 100644
--- a/modules/generative_grammar/generator.h
+++ b/modules/generative_grammar/generator.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "generative_grammar/symbol.h"
+#include "generative_grammar/grammar.h"
 #include "scene/3d/node_3d.h"
 
 class Generator : public Node3D {
@@ -12,8 +12,9 @@ protected:
 	void _notification(int what);
 
 public:
-	Ref<Symbol> state{};
+	Ref<Sentence> state{};
+	Rule *rule{ nullptr };
 
 private:
-	GET_SET_FNS(Ref<Symbol>, state);
+	GET_SET_FNS(Ref<Sentence>, state);
 };
diff --git a/modules/generative_grammar/grammar.cpp b/modules/generative_grammar/grammar.cpp
index d00c925258..9b7fbcedb0 100644
--- a/modules/generative_grammar/grammar.cpp
+++ b/modules/generative_grammar/grammar.cpp
@@ -1,25 +1,156 @@
 #include "generative_grammar/grammar.h"
 #include "core/object/class_db.h"
+#include "core/variant/typed_array.h"
 #include "macros.h"
 
 void Sentence::_bind_methods() {
-	BIND_PROPERTY(Variant::STRING, symbols_string);
-	BIND_PROPERTY(Variant::INT, width);
+	BIND_HPROPERTY(Variant::STRING, symbols_string, PROPERTY_HINT_MULTILINE_TEXT);
+	BIND_PROPERTY(Variant::VECTOR2I, size);
 }
 
 bool Sentence::is_terminal() const {
-	for (char32_t c : this->symbols) {
-		if (String::char_uppercase(c)) {
+	for (Symbol c : this->symbols) {
+		if (!symbol_is_terminal(c)) {
 			return false;
 		}
 	}
 	return true; // no non-terminals in sentence
 }
 
-void Rule::_bind_methods() {
+Symbol Sentence::get_at(Vector2i coord) const {
+	int idx{ coord.x + (coord.y * this->size.x) };
+	ERR_FAIL_COND_V_EDMSG(idx < this->symbols.size(), NonTerminals::Invalid, "Sentence::get_at: invalid coordinate");
+	return this->symbols.get(idx);
+}
+
+void Sentence::set_at(Vector2i coord, Symbol symbol) {
+	int idx{ coord.x + (coord.y * this->size.x) };
+	ERR_FAIL_COND_EDMSG(idx < this->symbols.size(), "Sentence::set_at: invalid coordinate");
+	this->symbols.set(idx, symbol);
+}
+
+bool Sentence::check_match_at(Vector2i at, Ref<Sentence> pattern) {
+	Vector2i const pattern_size{ pattern->get_size() };
+	if (at.x + pattern_size.x > this->size.x || at.y + pattern_size.y > this->size.y) {
+		return false; // can't match, out of bounds
+	}
+	for (Vector2i itr{ 0, 0 }; itr.y < pattern_size.x; ++itr.y) {
+		for (; itr.x + at.x < pattern_size.x; ++itr.x) {
+			if (get_at(at + itr) != pattern->get_at(itr)) {
+				return false; // difference found
+			}
+		}
+		itr.x = at.x;
+	}
+	return true;
+}
+
+void Sentence::write_subsentence(Vector2i at, Ref<Sentence> sentence) {
+	for (Vector2i pos{ 0, 0 }; pos.y < sentence->get_size().y; ++pos.y) {
+		for (; pos.x < sentence->get_size().x; ++pos.x) {
+			set_at(at + pos, sentence->get_at(pos));
+		}
+		pos.x = 0;
+	}
+}
+
+void Sentence::set_symbols_string(String value) {
+	int size{ this->size.x * this->size.y };
+	int writer{ 0 };
+	for (int reader{ 0 }; writer < size; ++reader) {
+		char32_t c{ value.length() >= reader ? value[reader] : (char32_t)'B' };
+		if (c != '\n') {
+			this->symbols.set(writer, c);
+			++writer;
+		}
+	}
+}
+
+String Sentence::get_symbols_string() const {
+	String value{};
+	for (int i{ 0 }; i < this->symbols.size(); ++i) {
+		if (i != 0 && i % this->size.x == 0) {
+			value += L'\n';
+		}
+		value += this->symbols.get(i);
+	}
+	return value;
+}
+
+void Sentence::set_size(Vector2i value) {
+	this->size = value;
+	this->symbols.clear();
+	this->symbols.resize_initialized(this->size.x * this->size.y);
+	for (int i{ 0 }; i < this->symbols.size(); ++i) {
+		this->symbols.set(i, 'B');
+	}
+}
+
+Vector2i Sentence::get_size() const {
+	return this->size;
+}
+
+void CompositeRule::_notification(int what) {
+	switch (what) {
+		case NOTIFICATION_READY:
+		case NOTIFICATION_CHILD_ORDER_CHANGED:
+			this->rules.clear();
+			for (Variant child : get_children()) {
+				if (Rule * rule{ cast_to<Rule>(child) }) {
+					this->rules.push_back(rule);
+				}
+			}
+			return;
+	}
+}
+
+void CompositeRule::try_apply(Ref<Sentence> sentence) {
+	for (Rule *rule : this->rules) {
+		rule->try_apply(sentence);
+	}
+}
+
+void ReplaceRule::_bind_methods() {
 	BIND_HPROPERTY(Variant::OBJECT, pattern, PROPERTY_HINT_RESOURCE_TYPE, Sentence::get_class_static());
 	BIND_HPROPERTY(Variant::OBJECT, result, PROPERTY_HINT_RESOURCE_TYPE, Sentence::get_class_static());
 }
 
-void Rule::try_apply(Ref<Sentence> sentence) {
+void ReplaceRule::try_apply(Ref<Sentence> sentence) {
+	Vector2i max{ sentence->get_size() - this->pattern->get_size() };
+	if (max.x < 0 || max.y < 0) {
+		return; // cannot continue, no area in sentence big enough
+	}
+	for (Vector2i pos{ 0, 0 }; pos.y < max.y; ++pos.y) {
+		for (; pos.x < max.x; ++pos.x) {
+			if (sentence->check_match_at(pos, this->pattern)) {
+				sentence->write_subsentence(pos, this->result);
+			}
+		}
+		pos.x = 0;
+	}
+}
+
+void ResizeRule::_bind_methods() {
+	BIND_PROPERTY(Variant::INT, factor);
+}
+
+void ResizeRule::fill_area(Ref<Sentence> data, Vector2i coord, Symbol tile) {
+	for (Vector2i at{ 0, 0 }; at.y < this->factor; ++at.y) {
+		for (; at.x < this->factor; ++at.x) {
+			data->set_at(coord * this->factor + at, tile);
+		}
+		at.x = 0;
+	}
+}
+
+void ResizeRule::try_apply(Ref<Sentence> sentence) {
+	Vector2i size_before{ sentence->size };
+	Vector<Symbol> before{ sentence->symbols };
+	sentence->set_size(size_before * this->factor);
+	for (Vector2i at{ 0, 0 }; at.y < size_before.y; ++at.y) {
+		for (; at.x < size_before.x; ++at.x) {
+			fill_area(sentence, at, before.get(at.x + at.y * size_before.x));
+		}
+		at.x = 0;
+	}
 }
diff --git a/modules/generative_grammar/grammar.h b/modules/generative_grammar/grammar.h
index a69c7d6bb5..b84e473d2b 100644
--- a/modules/generative_grammar/grammar.h
+++ b/modules/generative_grammar/grammar.h
@@ -1,7 +1,23 @@
 #pragma once
 
-#include "core/io/resource.h"
 #include "macros.h"
+#include "scene/main/node.h"
+
+typedef char32_t Symbol;
+
+namespace NonTerminals {
+enum : Symbol {
+	Start = 'S',
+	Blocked = 'B',
+	Invalid = '!',
+};
+};
+
+namespace Terminals {
+enum : Symbol {
+	Invalid = '!',
+};
+};
 
 class Sentence : public Resource {
 	GDCLASS(Sentence, Resource);
@@ -9,24 +25,54 @@ class Sentence : public Resource {
 
 public:
 	bool is_terminal() const;
+	Symbol get_at(Vector2i coord) const;
+	void set_at(Vector2i coord, Symbol symbol);
+	bool check_match_at(Vector2i at, Ref<Sentence> pattern);
+	void write_subsentence(Vector2i at, Ref<Sentence> sentence);
+	static bool symbol_is_terminal(Symbol symbol) {
+		return String::char_lowercase(symbol) == symbol;
+	}
 
-private:
-	Vector<char32_t> symbols{};
-	int width{ 0 };
+public:
+	Vector<Symbol> symbols{};
+	Vector2i size{ 0, 0 };
 
 public:
 	void set_symbols_string(String value);
 	String get_symbols_string() const;
-	void set_width(int width);
-	int get_width() const;
+	void set_size(Vector2i width);
+	Vector2i get_size() const;
 };
 
-struct Rule : public Resource {
-	GDCLASS(Rule, Resource);
+class Rule : public Node {
+	GDCLASS(Rule, Node);
+	static void _bind_methods() {}
+
+public:
+	virtual void try_apply(Ref<Sentence> graph) {}
+};
+
+class CompositeRule : public Rule {
+	GDCLASS(CompositeRule, Rule);
+	static void _bind_methods() {}
+	void order_changed();
+
+protected:
+	void _notification(int what);
+
+public:
+	void try_apply(Ref<Sentence> graph) override;
+
+protected:
+	Vector<Rule *> rules{};
+};
+
+class ReplaceRule : public Rule {
+	GDCLASS(ReplaceRule, Rule);
 	static void _bind_methods();
 
 public:
-	void try_apply(Ref<Sentence> graph);
+	void try_apply(Ref<Sentence> graph) override;
 
 private:
 	Ref<Sentence> pattern{};
@@ -36,3 +82,23 @@ public:
 	GET_SET_FNS(Ref<Sentence>, pattern);
 	GET_SET_FNS(Ref<Sentence>, result);
 };
+
+class ResizeRule : public CompositeRule {
+	GDCLASS(ResizeRule, Rule);
+	static void _bind_methods();
+	void fill_area(Ref<Sentence> data, Vector2i coord, Symbol tile);
+
+public:
+	void try_apply(Ref<Sentence> sentence) override;
+
+private:
+	int factor{ 10 };
+
+public:
+	GET_SET_FNS(int, factor);
+};
+
+class PickRandomRule : public CompositeRule {
+	GDCLASS(PickRandomRule, CompositeRule);
+	static void _bind_methods() {}
+};
diff --git a/modules/generative_grammar/register_types.cpp b/modules/generative_grammar/register_types.cpp
index 62f15d8de6..69f63c02a9 100644
--- a/modules/generative_grammar/register_types.cpp
+++ b/modules/generative_grammar/register_types.cpp
@@ -1,14 +1,16 @@
 #include "generative_grammar/register_types.h"
 #include "core/object/class_db.h"
 #include "generative_grammar/generator.h"
-#include "generative_grammar/symbol.h"
+#include "generative_grammar/grammar.h"
 
 void initialize_generative_grammar_module(ModuleInitializationLevel p_level) {
 	if (p_level != MODULE_INITIALIZATION_LEVEL_SCENE) {
 		return;
 	}
-	ClassDB::register_class<Symbol>();
-	ClassDB::register_class<Rule>();
+	ClassDB::register_abstract_class<Rule>();
+	ClassDB::register_class<Sentence>();
+	ClassDB::register_class<CompositeRule>();
+	ClassDB::register_class<ReplaceRule>();
 	ClassDB::register_class<Generator>();
 }
 
diff --git a/project/data/rules/test_rule.tres b/project/data/rules/test_rule.tres
deleted file mode 100644
index 8f5fcf78b9..0000000000
--- a/project/data/rules/test_rule.tres
+++ /dev/null
@@ -1,13 +0,0 @@
-[gd_resource type="Rule" format=3 uid="uid://cb5x75r5umlh5"]
-
-[sub_resource type="Symbol" id="Symbol_26ujg"]
-
-[sub_resource type="Symbol" id="Symbol_titn7"]
-type = 1
-
-[sub_resource type="Symbol" id="Symbol_kwj57"]
-children_array = Array[Object]([SubResource("Symbol_titn7")])
-
-[resource]
-match = SubResource("Symbol_26ujg")
-result = SubResource("Symbol_kwj57")
diff --git a/project/scenes/levels/dungeon.tscn b/project/scenes/levels/dungeon.tscn
index 269690c8c0..ec3dcbd7dc 100644
--- a/project/scenes/levels/dungeon.tscn
+++ b/project/scenes/levels/dungeon.tscn
@@ -1,8 +1,16 @@
 [gd_scene format=3 uid="uid://cak2tf2adjv8j"]
 
-[sub_resource type="Symbol" id="Symbol_bb2w7"]
+[sub_resource type="Sentence" id="Sentence_bb2w7"]
+symbols_string = "BBBBB
+BBBBB
+BBBBB
+BBBBB
+BBBBB"
+size = Vector2i(5, 5)
 
 [node name="Dungeon" type="Node3D" unique_id=719313039]
 
 [node name="Generator" type="Generator" parent="." unique_id=1532743122]
-state = SubResource("Symbol_bb2w7")
+state = SubResource("Sentence_bb2w7")
+
+[node name="ReplaceRule" type="ReplaceRule" parent="Generator" unique_id=1787373751]