I've had a little discussion with one of my co-workers regarding how to handle the Clear all -button in a mandatory input-field on the iPhone. The field holds the account email address and is present in the Account information view in our app. Changes in the view can not be saved if the user hasn't provided a valid email address.
Here it is depicted if you don't follow which button I mean:
Here is how the two opinions has been reasoned:
One side argues that the button should be removed because the field is required, and providing a Clear All -action could cue to a user that the field could be left empty, "why else would we provide such an action"? Only power users will note that it's gone and they will then without thinking select the entire text with double tap for instant erase.
One side argues that the button should be kept. This is what the user expects and by that consistency is withheld. Removing it would hinder a users sense of control and compromise interactive capabilities. The user could still with the Clear button removed, backspace all text and then be annoyed that they can't save their changes, removing the Clear all button will not work around that.
Do any of you have any good input on either of the opinions mentioned? Personal preference should be kept to a minimum, unless it can be reasoned in a way that totally differs from how it's reasoned in the points above. If you can provide any unique hard evidence for either of the points then you get a star! (well, not really, but most probably an instant upvote!)