It's ok to have 1-3 spaces (but never >= 4) after the last leading tab if it makes it look prettier, but in this case, we have 

`<tab><tab><tab><sp><sp><sp><sp><sp><sp>`. The first four `<sp>` should be replaced with `<tab>`.

However, in this case, 0 trailing spaces is really better. One case I can think of where it is legitimate to have 1-3 spaces after a leading tab, it to line up attributes on an endpoint, such as

````
<service-activator input-channel="foo"
                           output-channel="bar"
                            ... />
````

I did a lot of cleanup in the 3.0 schemas, but I might have missed some.