layers and z

examples/basic.py

@@ -10,11 +10,13 @@ class BasicApp(App):
     App > DockView {
         layout: dock;
         docks: sidebar=left widgets=top;
+        layers: base panels;
     }
 
     #sidebar {
         dock-group: sidebar;
         width: 40;
+        layer: panels;
     }
 
     #widget1 {

src/textual/css/_style_properties.py

@@ -312,7 +312,7 @@ class NameProperty:
         self._internal_name = f"_rule_{name}"
 
     def __get__(self, obj: Styles, objtype: type[Styles] | None) -> str:
-        return getattr(obj, self._internal_name, None) or ""
+        return getattr(obj, self._internal_name) or ""
 
     def __set__(self, obj: Styles, name: str | None) -> str | None:
         if not isinstance(name, str):

src/textual/css/_styles_builder.py

@@ -320,3 +320,16 @@ class StylesBuilder:
             self.styles.dock_edge = tokens[0].value if tokens else ""
         except StyleValueError as error:
             self.error(name, tokens[0], str(error))
+
+    def process_layer(self, name: str, tokens: list[Token]) -> None:
+        if len(tokens) > 1:
+            self.error(name, tokens[1], f"unexpected tokens in dock-edge declaration")
+        self.styles._rule_layer = tokens[0].value
+
+    def process_layers(self, name: str, tokens: list[Token]) -> None:
+        layers: list[str] = []
+        for token in tokens:
+            if token.name != "token":
+                self.error(name, token, "{token.name} not expected here")
+            layers.append(token.value)
+        self.styles._rule_layers = tuple(layers)

src/textual/css/match.py

@@ -8,11 +8,10 @@ if TYPE_CHECKING:
     from ..dom import DOMNode
 
 
-def match(selector_sets: Iterable[SelectorSet], node: DOMNode):
-    for selector_set in selector_sets:
-        if _check_selectors(selector_set.selectors, node):
-            return True
-    return False
+def match(selector_sets: Iterable[SelectorSet], node: DOMNode) -> bool:
+    return any(
+        _check_selectors(selector_set.selectors, node) for selector_set in selector_sets
+    )
 
 
 def _check_selectors(selectors: list[Selector], node: DOMNode) -> bool:

src/textual/css/model.py

@@ -32,10 +32,6 @@ class Location:
     column: tuple[int, int]
 
 
-def _default_check(node: DOMNode) -> bool | None:
-    return True
-
-
 @dataclass
 class Selector:
     name: str
@@ -67,27 +63,27 @@ class Selector:
             SelectorType.ID: self._check_id,
         }
 
-    def check(self, node: DOMNode) -> bool | None:
+    def check(self, node: DOMNode) -> bool:
         return self._checks[self.type](node)
 
-    def _check_universal(self, node: DOMNode) -> bool | None:
+    def _check_universal(self, node: DOMNode) -> bool:
         return True
 
-    def _check_type(self, node: DOMNode) -> bool | None:
+    def _check_type(self, node: DOMNode) -> bool:
         if node.css_type != self._name_lower:
             return False
         if self.pseudo_classes and not node.has_psuedo_class(*self.pseudo_classes):
             return False
         return True
 
-    def _check_class(self, node: DOMNode) -> bool | None:
+    def _check_class(self, node: DOMNode) -> bool:
         if not node.has_class(self._name_lower):
             return False
         if self.pseudo_classes and not node.has_psuedo_class(*self.pseudo_classes):
             return False
         return True
 
-    def _check_id(self, node: DOMNode) -> bool | None:
+    def _check_id(self, node: DOMNode) -> bool:
         if not node.id == self._name_lower:
             return False
         if self.pseudo_classes and not node.has_psuedo_class(*self.pseudo_classes):
@@ -110,9 +106,8 @@ class SelectorSet:
 
     def __post_init__(self) -> None:
         SAME = CombinatorType.SAME
-        # self.selectors[-1].advance = 1
         for selector, next_selector in zip(self.selectors, self.selectors[1:]):
-            selector.advance = 0 if next_selector.combinator == SAME else 1
+            selector.advance = int(next_selector.combinator != SAME)
 
     def __rich_repr__(self) -> rich.repr.Result:
         selectors = RuleSet._selector_to_css(self.selectors)
@@ -157,6 +152,11 @@ class RuleSet:
 
     @property
     def css(self) -> str:
+        """Generate the CSS this RuleSet
+
+        Returns:
+            str: A string containing CSS code.
+        """
         declarations = "\n".join(f"    {line}" for line in self.styles.css_lines)
         css = f"{self.selectors} {{\n{declarations}\n}}"
         return css

src/textual/css/styles.py

@@ -74,8 +74,8 @@ class Styles:
     _rule_dock_edge: str | None = None
     _rule_docks: tuple[tuple[str, str], ...] | None = None
 
-    _rule_layers: str | None = None
-    _rule_layer: tuple[str, ...] | None = None
+    _rule_layers: tuple[str, ...] | None = None
+    _rule_layer: str | None = None
 
     important: set[str] = field(default_factory=set)
 

src/textual/dom.py

@@ -17,6 +17,10 @@ if TYPE_CHECKING:
     from .widget import Widget
 
 
+class NoParent(Exception):
+    pass
+
+
 @rich.repr.auto
 class DOMNode(MessagePump):
     """A node in a hierarchy of things forming the UI.
@@ -39,6 +43,13 @@ class DOMNode(MessagePump):
         if self._classes:
             yield "classes", self._classes
 
+    @property
+    def parent(self) -> DOMNode:
+        if self._parent is None:
+            raise NoParent(f"{self._parent} has no parent")
+        assert isinstance(self._parent, DOMNode)
+        return self._parent
+
     @property
     def id(self) -> str | None:
         return self._id
@@ -84,6 +95,27 @@ class DOMNode(MessagePump):
     def visible(self) -> bool:
         return self.styles.display != "none"
 
+    @property
+    def z(self) -> tuple[int, ...]:
+        """Get the z index tuple for this node.
+
+        Returns:
+            tuple[int, ...]: A tuple of ints to sort layers by.
+        """
+        indexes: list[int] = []
+        append = indexes.append
+        node = self
+        while node._parent:
+            styles = node.styles
+            parent_styles = node.parent.styles
+            append(
+                parent_styles.layers.index(styles.layer)
+                if styles.layer in parent_styles.layers
+                else 0
+            )
+            node = node.parent
+        return tuple(reversed(indexes))
+
     @property
     def tree(self) -> Tree:
         highlighter = ReprHighlighter()

src/textual/message_pump.py

@@ -48,10 +48,8 @@ class MessagePump:
         return self._task
 
     @property
-    def parent(self) -> MessagePump:
-        if self._parent is None:
-            raise NoParent(f"{self._parent} has no parent")
-        return self._parent
+    def has_parent(self) -> bool:
+        return self._parent is not None
 
     @property
     def app(self) -> "App":