The new technique avoids various problems with any text-indent method.
The benefits are:
* No box of any kind is drawn offscreen, so there is no risk of
related performance problems in old iOS devices.
* No need to specify a text-alignment and hide overflow since the text
is crushed to take up no space.
* No need to hide `br` or make all fallback HTML `display:inline`
because unlike the text-indent approaches, this method is not
affected by those scenarios.
* Fewer styles are needed as a result of these improvements.
The function of the new CSS is as follows:
* `font: 0/0 a` is a shorthand property that reduces the font-size and
line-height to 0. The `a` value acts as a font-family. The CSS
validator complains that using `0/0` in the shorthand `font` property
is not valid, but every browser accepts it.
* `text-shadow: none` makes sure than any inherited text shadow is
removed, otherwise it will show over the image.
* `color: transparent` is only really needed in browsers than don't
completely crush the text to the point of being invisible. Safari 4 is
such a browser (but extremely rare). Leaving it in for now in case
there are any mobile browsers that require it. Upon further testing,
it may be possible to remove this declaration.
Some parts of the pre-existing image replacement technique have been
retained. The border and background resets are useful when using IR on
form submit inputs or buttons, as well as when links use default borders