Use cases for title attribute on img element?

Hi

I'm pretty new at working with the Drupal API. Developing on D6, I've noticed that the core theme_image() function will output an empty title attribute value if none is supplied, e.g.

<img src="myimage.png" alt="my image description" title="" />
(In the case of @alt, blank is actually a good default BTW.)

I could see this being a problem if the image is hyperlinked, where the link itself uses a title attribute, e.g.

This actually happens when invoking the standard views_handler_field_contact_link->render() method from the core Contact module's views handlers when you choose to render a contact link as a mail icon:

Which title attribute does the browser render, the outer or the inner? I'm into standards more than user agent testing, but my Firefox 6 and Konqueror thankfully do what I want and render the outer @title as a tooltip. However, I don't like taking unnecessary risks with this kind of ambiguous markup. Who knows what some weird and wonderful devices and user agents might make of this? A semantically-augmented accessibility red light goes on.

It leads me to ask why a @title would be needed on an image. I know it's totally valid (doctype-wise) and distinct from @alt, but what's a use case for img/@title outside of when it's hyperlinked?

I notice the 7 & 8 APIs will not output an attribute if not supplied as an argument. That's good, but the APIs still kind of elevate @title to a first class attribute on <img/>, by virtue of including it as an enumerated key in $variables. That is, it's treated like @src, @alt, @width, and @height. I can imagine this leading developers to thinking they should include this attribute when they invoke theme_image().

If we can't find a good use case for img/@title, should we take 'title' out of the enumerated keys in $variables in D8?

Further, would it be a good idea to somehow fail or warn when @alt is not supplied? It is a required attribute according to the doctype. As D7 & D8 have it, the attribute is not present when not supplied. I don't know what the Drupalest way to handle this is, just throwing it out there as something we might catch in some way. Drupal's philosophy on handling/preventing such errors is unknown to me.

Cheers