[Bug 17152] Support centering an element when scrolling into view.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=17152

--- Comment #5 from Thaddee TYL <thaddee.tyl@gmail.com> ---
(In reply to comment #4)
> (In reply to comment #0)
> > As a result, what authors really want is to center
> > the element.
> 
> If that's what authors want, why does the proposal do more than that? What's
> the use case for arbitrary positioning? What's the use case for
> `evenIfViewed`?

There are two reasons to use this.

One is to perform search. In that case, preserving the surroundings of the
element that currently matched (in a series of matches) allows the user to see
in which context the element is. A common UI decision in this case is to
highlight the element in some way. As a result, it is not necessary to actually
bring the element at the center of the viewport; furthermore, not changing the
viewport allows the user to see the spatial relationship between the element
that currently match with the next one in the list. In this case, the author
will probably want to set `evenIfViewed` to false.

The other one is simply to bring an element into the viewport. In that case,
there is no list of matches, we simply want to force a certain element into the
viewport in a specific way. The author will then want to set `evenIfViewed` to
true.

In that latter case, the author may also want to position the element in a
different way than simply centering the element in the viewport. For instance,
if the bottom of the element is what is relevant for the user, it must be
shown. If the element is too big vertically for the viewport, the author may
want to set `vertical` to 1, to force the bottom of the element into view.

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Received on Tuesday, 14 May 2013 20:00:38 UTC