How to detect when the mouse button is being held down while the cursor is inside a collider?

Questions & Answers
1

I know that if I use OnMouse down, Unity can register individual clicks inside a collider, but how can Unity detect if the mouse button is being held down inside a collider?

2

Use OnMouseEnter()

Called when the mouse enters the
GUIElement or Collider. The
corresponding OnMouseOver function is
called while the mouse stays over the
object and OnMouseExit is called when
it moves away.