diff --git a/export_presets.cfg b/export_presets.cfg
index d8bd5b8..adb2dc7 100644
--- a/export_presets.cfg
+++ b/export_presets.cfg
@@ -9,7 +9,7 @@ custom_features=""
 export_filter="all_resources"
 include_filter=""
 exclude_filter="builds/*,playtest/*,scripts/*"
-export_path="builds/v0.3.0-prealpha.2/windows-x86_64/NETfishing.exe"
+export_path="builds/v0.3.0-prealpha.3/windows-x86_64/NETfishing.exe"
 patches=PackedStringArray()
 encryption_include_filters=""
 encryption_exclude_filters=""
@@ -35,11 +35,11 @@ application/modify_resources=true
 application/icon=""
 application/console_wrapper_icon=""
 application/icon_interpolation=4
-application/file_version="0.3.0.2"
-application/product_version="0.3.0.2"
+application/file_version="0.3.0.3"
+application/product_version="0.3.0.3"
 application/company_name=""
 application/product_name="NETfishing"
-application/file_description="NETfishing v0.3.0-prealpha.2"
+application/file_description="NETfishing v0.3.0-prealpha.3"
 application/copyright=""
 application/trademarks=""
 application/export_angle=0
@@ -62,7 +62,7 @@ custom_features=""
 export_filter="all_resources"
 include_filter=""
 exclude_filter="builds/*,playtest/*,scripts/*"
-export_path="builds/v0.3.0-prealpha.2/linux-x86_64/NETfishing.x86_64"
+export_path="builds/v0.3.0-prealpha.3/linux-x86_64/NETfishing.x86_64"
 patches=PackedStringArray()
 encryption_include_filters=""
 encryption_exclude_filters=""
diff --git a/network/player_data_root.gd b/network/player_data_root.gd
index 37983fd..c0fe26e 100644
--- a/network/player_data_root.gd
+++ b/network/player_data_root.gd
@@ -14,6 +14,9 @@ const README_FILENAME := "README.txt"
 const ENVIRONMENT_VARIABLE := "NETFISHING_DATA_DIR"
 const APPLICATION_ID := "netfishing"
 const APP_DATA_PORTABLE_PATH := "user://portable-data"
+const PATH_ALLOWED: StringName = &"allowed"
+const PATH_SOURCE_PROJECT: StringName = &"source_project"
+const PATH_INSTALLATION: StringName = &"installation"
 
 enum Mode {
 	UNRESOLVED,
@@ -226,15 +229,77 @@ func _activate_existing(path: String, expected_id: String, permit_creation: bool
 
 
 func _validate_candidate(path: String, create: bool) -> bool:
-	if path.is_empty() or not path.is_absolute_path():
+	var normalized: String = _normalize(path)
+	if normalized.is_empty() or not normalized.is_absolute_path():
 		return _fail("Choose an absolute filesystem folder.")
-	var project: String = ProjectSettings.globalize_path("res://").trim_suffix("/")
-	if path == project or path.begins_with(project + "/"):
+	var classification: StringName = classify_candidate_path(
+		normalized,
+		ProjectSettings.globalize_path("res://"),
+		OS.get_executable_path().get_base_dir(),
+	)
+	if classification == PATH_SOURCE_PROJECT:
 		return _fail("The project folder cannot be used as the player data folder.")
-	if not DirAccess.dir_exists_absolute(path):
-		if not create or DirAccess.make_dir_recursive_absolute(path) != OK:
+	if classification == PATH_INSTALLATION:
+		return _fail(
+			"The application installation folder cannot be used as the player data folder."
+		)
+	if not DirAccess.dir_exists_absolute(normalized):
+		if not create or DirAccess.make_dir_recursive_absolute(normalized) != OK:
 			return _fail("The selected data folder is unavailable.")
-	return _test_writable(path)
+	return _test_writable(normalized)
+
+
+static func classify_candidate_path(
+	candidate_path: String,
+	project_reference: String,
+	installation_reference: String,
+	case_insensitive: bool = OS.get_name() == "Windows",
+) -> StringName:
+	var candidate: String = _normalize_comparison_path(
+		candidate_path, case_insensitive
+	)
+	if candidate.is_empty() or not candidate.is_absolute_path():
+		return PATH_ALLOWED
+	var project: String = _normalize_reference_path(
+		project_reference, case_insensitive
+	)
+	if not project.is_empty() and _is_same_or_child_path(candidate, project):
+		return PATH_SOURCE_PROJECT
+	var installation: String = _normalize_reference_path(
+		installation_reference, case_insensitive
+	)
+	if (
+		not installation.is_empty()
+		and _is_same_or_child_path(candidate, installation)
+	):
+		return PATH_INSTALLATION
+	return PATH_ALLOWED
+
+
+static func _normalize_reference_path(path: String, case_insensitive: bool) -> String:
+	var normalized: String = _normalize_comparison_path(path, case_insensitive)
+	if normalized.is_empty() or not normalized.is_absolute_path():
+		return ""
+	if normalized == "/" or _is_windows_drive_root(normalized):
+		return ""
+	return normalized
+
+
+static func _normalize_comparison_path(path: String, case_insensitive: bool) -> String:
+	var normalized: String = path.strip_edges().replace("\\", "/").simplify_path()
+	while normalized.length() > 1 and normalized.ends_with("/"):
+		if _is_windows_drive_root(normalized):
+			break
+		normalized = normalized.left(-1)
+	return normalized.to_lower() if case_insensitive else normalized
+
+
+static func _is_windows_drive_root(path: String) -> bool:
+	return path.length() == 3 and path[1] == ":" and path[2] == "/"
+
+
+static func _is_same_or_child_path(candidate: String, reference: String) -> bool:
+	return candidate == reference or candidate.begins_with(reference + "/")
 
 
 func _test_writable(path: String) -> bool:
@@ -340,7 +405,12 @@ func _directory_is_empty(path: String) -> bool:
 
 
 func _normalize(path: String) -> String:
-	return path.simplify_path().trim_suffix("/")
+	var normalized: String = path.replace("\\", "/").simplify_path()
+	while normalized.length() > 1 and normalized.ends_with("/"):
+		if _is_windows_drive_root(normalized):
+			break
+		normalized = normalized.left(-1)
+	return normalized
 
 
 func _read_json(path: String, maximum := 1024 * 1024) -> Dictionary:
diff --git a/playtest/README-PLAYTEST.txt b/playtest/README-PLAYTEST.txt
index 5c93144..590da0f 100644
--- a/playtest/README-PLAYTEST.txt
+++ b/playtest/README-PLAYTEST.txt
@@ -1,5 +1,5 @@
 NETfishing
-v0.3.0-prealpha.2
+v0.3.0-prealpha.3
 Pre-Alpha 0.3
 
 Thank you for trying this early private playtest.
diff --git a/project.godot b/project.godot
index c2b8990..94a8d73 100644
--- a/project.godot
+++ b/project.godot
@@ -11,7 +11,7 @@ config_version=5
 [application]
 
 config/name="NETFISHING"
-config/version="0.3.0-prealpha.2"
+config/version="0.3.0-prealpha.3"
 run/main_scene="res://main/main.tscn"
 config/features=PackedStringArray("4.7", "GL Compatibility")
 config/icon="res://icon.svg"
diff --git a/scripts/build_playtest.sh b/scripts/build_playtest.sh
index d82ee16..74bbece 100755
--- a/scripts/build_playtest.sh
+++ b/scripts/build_playtest.sh
@@ -4,12 +4,12 @@ set -euo pipefail
 
 readonly SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 readonly PROJECT_ROOT="$(cd -- "${SCRIPT_DIR}/.." && pwd)"
-readonly BUILD_ROOT="${PROJECT_ROOT}/builds/v0.3.0-prealpha.2"
+readonly BUILD_ROOT="${PROJECT_ROOT}/builds/v0.3.0-prealpha.3"
 readonly WINDOWS_DIR="${BUILD_ROOT}/windows-x86_64"
 readonly LINUX_DIR="${BUILD_ROOT}/linux-x86_64"
 readonly README_SOURCE="${PROJECT_ROOT}/playtest/README-PLAYTEST.txt"
-readonly WINDOWS_ZIP="${BUILD_ROOT}/NETfishing-v0.3.0-prealpha.2-windows-x86_64.zip"
-readonly LINUX_ZIP="${BUILD_ROOT}/NETfishing-v0.3.0-prealpha.2-linux-x86_64.zip"
+readonly WINDOWS_ZIP="${BUILD_ROOT}/NETfishing-v0.3.0-prealpha.3-windows-x86_64.zip"
+readonly LINUX_ZIP="${BUILD_ROOT}/NETfishing-v0.3.0-prealpha.3-linux-x86_64.zip"
 readonly GODOT_BIN="${GODOT_BIN:-godot}"
 
 if [[ ! -f "${PROJECT_ROOT}/project.godot" ]]; then
diff --git a/scripts/test_player_data_root_paths.gd b/scripts/test_player_data_root_paths.gd
new file mode 100644
index 0000000..69a2485
--- /dev/null
+++ b/scripts/test_player_data_root_paths.gd
@@ -0,0 +1,130 @@
+extends SceneTree
+
+const PROJECT_PATH := "/tmp/netfishing"
+const INSTALL_PATH := "/opt/NETfishing"
+
+
+func _initialize() -> void:
+	var root_to_create: String = OS.get_environment("NETFISHING_TEST_CREATE_ROOT")
+	if not root_to_create.is_empty():
+		_create_validation_root(root_to_create)
+		return
+	var failures: PackedStringArray = []
+	_expect(
+		"external temporary directory",
+		"/tmp/NETfishing-test-data",
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect(
+		"external trailing slash",
+		"/tmp/NETfishing-test-data/",
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect(
+		"similar project-name sibling",
+		"/tmp/netfishing-data",
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect(
+		"documents directory",
+		"/home/player/Documents/NETfishing",
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect("source project", PROJECT_PATH, PlayerDataRoot.PATH_SOURCE_PROJECT, failures)
+	_expect(
+		"source project child",
+		PROJECT_PATH.path_join("player-data"),
+		PlayerDataRoot.PATH_SOURCE_PROJECT,
+		failures,
+	)
+	_expect(
+		"installation directory",
+		INSTALL_PATH,
+		PlayerDataRoot.PATH_INSTALLATION,
+		failures,
+	)
+	_expect(
+		"installation child",
+		INSTALL_PATH.path_join("portable-data"),
+		PlayerDataRoot.PATH_INSTALLATION,
+		failures,
+	)
+	_expect_with_references(
+		"empty project reference",
+		"/tmp/NETfishing-test-data",
+		"",
+		INSTALL_PATH,
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect_with_references(
+		"root project reference",
+		"/tmp/NETfishing-test-data",
+		"/",
+		INSTALL_PATH,
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+	)
+	_expect_with_references(
+		"Windows component and case normalization",
+		"C:\\Games\\NETfishing Data",
+		"C:\\Games\\NETfishing",
+		"C:\\Program Files\\NETfishing",
+		PlayerDataRoot.PATH_ALLOWED,
+		failures,
+		true,
+	)
+	if failures.is_empty():
+		print("PlayerDataRoot path validation: PASS")
+		quit(0)
+		return
+	for failure: String in failures:
+		push_error(failure)
+	quit(1)
+
+
+func _create_validation_root(path: String) -> void:
+	var data_root := PlayerDataRoot.new()
+	get_root().add_child(data_root)
+	if data_root.select_new_root(path):
+		print("PlayerDataRoot validation root created: ", data_root.root_path)
+		quit(0)
+		return
+	push_error(data_root.error_message)
+	quit(1)
+
+
+func _expect(
+	label: String,
+	candidate: String,
+	expected: StringName,
+	failures: PackedStringArray,
+) -> void:
+	_expect_with_references(
+		label,
+		candidate,
+		PROJECT_PATH,
+		INSTALL_PATH,
+		expected,
+		failures,
+	)
+
+
+func _expect_with_references(
+	label: String,
+	candidate: String,
+	project: String,
+	installation: String,
+	expected: StringName,
+	failures: PackedStringArray,
+	case_insensitive: bool = false,
+) -> void:
+	var actual: StringName = PlayerDataRoot.classify_candidate_path(
+		candidate, project, installation, case_insensitive
+	)
+	if actual != expected:
+		failures.append("%s: expected %s, got %s" % [label, expected, actual])
diff --git a/scripts/test_player_data_root_paths.gd.uid b/scripts/test_player_data_root_paths.gd.uid
new file mode 100644
index 0000000..90f8e0b
--- /dev/null
+++ b/scripts/test_player_data_root_paths.gd.uid
@@ -0,0 +1 @@
+uid://e8glhlm205au
diff --git a/ui/title_screen.tscn b/ui/title_screen.tscn
index 8fe3ddc..4a7c763 100644
--- a/ui/title_screen.tscn
+++ b/ui/title_screen.tscn
@@ -206,7 +206,7 @@ unique_name_in_owner = true
 layout_mode = 2
 theme_override_colors/font_color = Color(0.682, 0.733, 0.761, 1)
 theme_override_font_sizes/font_size = 22
-text = "v0.3.0-prealpha.2"
+text = "v0.3.0-prealpha.3"
 horizontal_alignment = 1
 
 [node name="Spacer" type="Control" parent="ResponsiveTitleStage/TitlePresentationScaleRoot/Center/MainContent"]