When set to false children of the owning RenderObject are allowed to
SemanticNodes of their parent with the semantic information
they want to contribute to the semantic tree.
When set to true the only way for children of the owning RenderObject
to contribute semantic information to the semantic tree is to introduce
SemanticNodes to the tree.
This setting is often used in combination with isSemanticBoundary to create semantic boundaries that are either writable or not for children.
bool explicitChildNodes = false