What a semantics node reports beyond its place, its name, its value and
its click: the properties few nodes set. A node holds them only when it
sets one, so a node without any stays small.
Semantic role describing how a node should participate in accessibility and hit testing.
Roles are now derived from SemanticsConfiguration rather than widget types.
Whether any box placed under root has area, as
build_layout_tree_from_applier would place it: the walk stops at the
first such box and reads no node’s modifiers or semantics.
The far right and bottom edges of the boxes with area placed under root,
measured from the root’s origin as build_layout_tree_from_applier
places them, reading no node’s modifiers or semantics. None while
nothing under root has area.
The modal the semantics tree of root would be rooted at, found without
building the tree: the topmost placed, visible modal that takes space,
or None when no modal is open. Unlike a tree update, it leaves the
nodes’ semantics dirty flags alone.
Check if a node or any of its descendants needs measure (selective measure optimization).
This can be used by the app shell to skip layout when the tree is clean.