The Three Tabindex Rules: 0, -1, and Never > 0

The tabindex HTML attribute controls programmatic and sequential focus behavior:

1. tabindex="0": Inserts an element into the natural keyboard tab order in its current DOM position. (Used when creating accessible custom interactive widgets).
2. tabindex="-1": Removes an element from the sequential keyboard tab order, but makes it programmatically focusable via JavaScript (element.focus()). (Used for modal containers, error alert banners, and custom roving focus widgets).
3. tabindex="1" or greater (POSITIVE TABINDEX):
   Strict Anti-Pattern: Positive tabindex values hijack the browser's tab flow, forcing focus to jump arbitrarily before all natural elements. Never use positive tabindex!