Committed as r1063

Changing to Fixed status with GWT 1.4 RC release

Unfortunately, this new behavior breaks our application at many places. We used setStyleName("") and 
removeStyleName(style) often to completely remove styles from elements. Although it is totally legal to have no 
class defined and an empty className property, this situation now leads to an Exception.

Please be aware that IE6 does not properly process multiple style names, thus the whole concept of adding and 
removing styles to a base style should not be forced.

We are reviewing this issue after having seeing some growing feedback that this
change is too inconvenient in its current form. We'll update this issue after a bit
more discussion on the contributors list.

@knorton: Could you clarify about IE not supporting multiple styles? My understanding
is that the IE limitation prevents you from writing single CSS selectors based on an
element having multiple types (i.e. the selector would have class names separated
with dots and no spaces). If that is true, then this is an opportunity to explain the
GWT recommended formulation of dependent style names (i.e. to make it easy to work
around the very IE bug in question).

I think here is a good explanation of the IE6 bug

<a href="http://www.ryanbrill.com/archives/multiple-classes-in-ie/">Multiple Classes in IE</a>

@rajeev: I've assigned this bug to you, because I believe you said you needed this
change as well. It should be a pretty simple change, as we discussed. Here's the last
thread I posted on the subject:

http://groups.google.com/group/Google-Web-Toolkit-Contributors/browse_thread/thread/6329f8f175590ce1

Thanks for the hyperlink. The lack of CSS selector support for multiple style names
was the behavior I was referring to. So, to clarify, IE will support multiple CSS
class names, but it won't properly apply a CSS selector that depends on two or more
class names being present simultaneously. I don't know if there's a term of this kind
of selector, but a good name might be an "intersection selector".

This bug was in fact a motivator for the best practice we wanted to encourage with
the introduction of dependent style names in GWT 1.4. By prefixing each dependent
style name with the common widget style name prefix, you can create families of
independent selectors that are clearly intended to be used together in concert.

IE6 does support multiple CSS classes on an element. What it doesn't support is multiple classes in a single 
CSS selector. Specifically, this is the situation it does not support:

<div class="foo bar"></div>

I can't select that with:
div.foo.bar {}

I can select it with both:
div.foo { }
div.bar { }

I don't see why this poses a problem to setStyleName, et. al. Those methods add/remove class names to the 
element, they do not do css selection and those elements are perfectly selectable by other CSS selectors. I 
don't find working around this particular selector to be any worse than working around any of the other 
selectors IE is missing.

Thanks for the clarification. I re-read your comments after some reading on the multiple class problems and 
doing some small experiments myself. There are so many bugs in IE CSS handling, that I seem to have mixed up 
something about the multiple class issues.

However, as already commented in the Group thread mentioned above, the main problem with the changes you 
did to the style related methods is that removeStyleName() throws an IllegalArgumentException if it is called to 
remove the last (base) style -- although that operation is absolutely legal from a CSS point of view.

@jgw: Assigning this one back to you. Based on the discussion today, it looks like
you'll be taking the lead on this one.

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I noticed that when I use a Grid cellformatter , that the setStyleName/getStyleName 
is implemented differently than in Widget setStyleName... now that is completely 
confusing!

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Committed as r1277.

1.4 RC2 now released.