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Class
SelectionChangingArgs
sealed
Vetoable payload of SelectionChanging. Subscribers inspect Proposed and may set Cancel to to block the selection change before it is applied.
Remarks
Reference type with a mutable
Cancel flag —.NET CancelEventArgs pattern. A fresh instance is allocated per SelectionChanging emission so subscribers can synchronously trigger another mutation from inside the handler (re-entrancy is safe). Veto fires only on user-driven mutations (click / move / extend / select-word etc.) — text-edit side effects use the internal non-vetoable path, so the selection hot path remains zero-alloc. Real use cases (P2.A atomic tokens, integrator-defined read-only ranges): block selection from landing inside an atomic pill, or constrain selection to stay within editable regions. Standard shouldX-pattern across UIKit (shouldChangeTextInRange), Web (beforeinput with preventDefault), WPF (PreviewKeyDown) — see D-010. UserEvent uses the same hierarchical strings as UserEvent.public TextSelection Previous{ get }Selection state before the change.
public TextSelection Proposed{ get; set }Selection state that will be applied if not cancelled.
Hierarchical category string — see SelectionChangedArgs.