Struct SequentialFocusNavigationSearch 

pub(crate) struct SequentialFocusNavigationSearch {
    focus_navigation_scope_owner: FocusNavigationScopeOwner,
    direction: SequentialFocusDirection,
    mechanism: SequentialFocusNavigationMechanism,
    starting_point: Option<DomRoot<Node>>,
    current_winner: Option<(DomRoot<Element>, i32)>,
    passed_starting_point: bool,
    search_context: SequentialFocusNavigationSearchContext,
}

This structure is used to do a traversal search of the DOM in order to find an appropriate target when doing sequential focus navigation, such as when handling tab key presses.

The specification talks about the flattened tabindex-ordered focus navigation scope, which represents all of the tabindex-ordered focus navigation scopes of a particular page, flattened into a single list of all the sequentially focusable areas of the page. Then, the specification describes how to search this list during sequential focus navigation.

The choice that Servo and other browsers make is to trade updating this flattened list during every DOM mutation (frequent) with a DOM traversal of, potentially, the entire document during sequential focus navigation (infrequent).

The search done via SequentialFocusNavigationSearch matches the semantics of the flattened tabindex-ordered focus navigation scope without having to maintain the flattened list. It uses a series of nested traversals (one per focus scope) that only considers each focusable area of a page at most once.

The search performs a linear DOM traversal starting at the containing focus scope of the search start point. When encountering a nested focus scope, if that scope could contain the final target for the search, the search recurses into the nested scope. If the search reaches the end of a focus scope without finding a candidate, the search continues in the focus scope’s containing scope (though never re-ascending back into a scope it recursed from).

Fields

focus_navigation_scope_owner: FocusNavigationScopeOwner

direction: SequentialFocusDirection

mechanism: SequentialFocusNavigationMechanism

starting_point: Option<DomRoot<Node>>

current_winner: Option<(DomRoot<Element>, i32)>

passed_starting_point: bool

search_context: SequentialFocusNavigationSearchContext

Implementations

impl SequentialFocusNavigationSearch

pub(crate) fn new( focus_navigation_scope_owner: FocusNavigationScopeOwner, direction: SequentialFocusDirection, mechanism: SequentialFocusNavigationMechanism, starting_point: Option<DomRoot<Node>>, ) -> Self

pub(crate) fn search(self) -> Option<DomRoot<Element>>

fn maybe_search_in_containing_focus_navigation_scope( &self, ) -> Option<DomRoot<Element>>

fn process_node(&mut self, node: &Node) -> Continue

fn process_node_as_sequentially_focusable_node( &mut self, node: &Node, ) -> Continue

If this node is sequentially focusable, consider whether or not to accept it as the new winner.

fn process_node_as_focus_scope_owner(&mut self, node: &Node) -> Continue

If this node itself forms a nested sequential focus scope, decide whether or not to descend and consider its contained focusable areas as candidates.

fn process_candidate_with_tab_index( &mut self, candidate_tab_index: i32, ) -> (bool, Continue)

Process the node or focus scope owner with the provided tab index according to this search’s search mechanism. Returns a boolean that is true if this candidate is the new winner and a Continue which says whether to keep searching or stop.

fn process_element_for_dom_traversal(&self) -> (bool, Continue)

Process the node or focus scope owner, given the state of Self::passed_starting_point with for searches with the SequentialFocusNavigationMechanism::Dom search mechanism. Returns a boolean that is true if this candidate is the new winner and a Continue which says whether to keep searching or stop.

fn process_element_for_first_or_last_traversal( &self, candidate_element_tab_index: i32, ) -> bool

Process the node or focus scope owner with the provided tab index for searches with the SequentialFocusNavigationMechanism::FirstOrLast search mechanism. Returns a boolean that is true if this candidate is the new winner.

fn process_element_for_sequential_traversal( &self, candidate_element_tab_index: i32, focused_element_tab_index: i32, ) -> (bool, Continue)

Process the node or focus scope owner with the provided tab index for searches with the SequentialFocusNavigationMechanism::Sequential search mechanism. Returns a boolean that is true if this candidate is the new winner and a Continue which says whether to keep searching or stop.