Checks if the argument is a valid Mathfield. After a Mathfield has been destroyed (for example by calling revertToOriginalContent() the Mathfield is no longer valid. However, there may be some pending operations invoked via requestAnimationFrame() for example, that would need to ensure the mathfield is still valid by the time they're executed.
nearestElementFromPoint(el: HTMLElement, x: number, y: number)private
Return a tuple of an element and a distance from point (x, y)
Utility function that returns the element which has the caret
Validate a style specification object