I don't recommend coding complex expressions in EL. Even if you have vast quantities of experience and know how the EL process works from the inside out (I do), debugging EL is a major pair in the sit-down-place. Plus, people routinely abuse it to break the separation between Model and View in MVC.
What my little XML snippet is intended to portray is a situation where the backing bean has to determine which styles to apply to the control. It's a lot easier to code and debug Java String expressions in a backing bean than it is in EL.
Also note that I used a style class instead of a brute-force style. That allows fine-tuning (and skinning!) the styling without requiring application code modifications, since only the CSS needs to be updated if you design the right set of style classes.
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