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# ->render()
 -  renders a radio tag with the value checked
 -  renders a radio tag using extra attributes
 -  considers false to be an integer 0
 -  considers true to be an integer 1
 -  returns an empty HTML string if no choices
# group support
 -  has support for groups
 -  throws an RuntimeException if you don't pass a choices option
# choices as a callable
 -  accepts a sfCallable as a choices option
# choices are translated
 -  translates the options
# choices are escaped
 -  escapes the choices
# __clone()
 -  changes the choices is a callable and the object is an instance of the current object
 -  changes nothing if the choices is a callable and the object is not an instance of the current object
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