The vast majority of web content existing today codes only to Mouse Events. The following describes an algorithm for how the user agent MAY map generic pointer input to mouse events for compatibility with this content.
The compatibility mapping with mouse events is an OPTIONAL feature of this specification. User agents are encouraged to support the feature for best compatibility with existing legacy content.
-Regardless of their support for compatibility mouse events, the user agents MUST always support the click, auxclick and contextmenu events because these events are of type PointerEvent and are therefore not compatibility mouse events. Calling preventDefault during a pointer event MUST NOT have an effect on whether click, auxclick, or contextmenu are fired or not.
Regardless of their support for compatibility mouse events, the user agents MUST always support the click, auxclick and contextmenu events because these events are of type PointerEvent and are therefore not compatibility mouse events. Calling preventDefault during a pointer event MUST NOT have an effect on whether click, auxclick, or contextmenu are fired or not.
The relative order of some of these high-level events (contextmenu, focus, blur, etc.) with pointer events is undefined and varies between user agents. For example, in some user agents contextmenu will often follow a {{GlobalEventHandlers/pointerup}}, while in others it'll often precede a {{GlobalEventHandlers/pointerup}} or {{GlobalEventHandlers/pointercancel}}, and in some situations it may be fired without any corresponding pointer event (for instance, as a result of a keyboard interaction).
In addition, user agents may apply their own heuristics to determine whether or not a click, auxclick, or contextmenu event should be fired. Some user agents may choose not to fire these events if there are other (non-primary) pointers of the same type, or other primary pointers of a different type. User agents may determine that a particular action was not a "clean" tap, click, or long-press (for instance, if an interaction with a finger on a touch screen includes too much movement while the finger is in contact with the screen) and decide not to fire a click, auxclick, or contextmenu event. These aspects of user agent behavior are not defined in this specification, and they may differ between implementations.