AX: HTML spec indicates @placeholder overrides @title for name computation, but WebKit only speaks placeholder when its visible. It should use the placeholder as the label if the field is not otherwise labeled, even when the placeholder is no longer visible.
<rdar://problem/16411745>
Some aspects of this name computation listing are wrong, but @placeholder seems logical. http://rawgithub.com/w3c/html-api-map/master/index.html#accessible-name-and-description-calculation