Following code will fail on JS validation (server validation is ok). On czech locale, the visible default value in input is actually 1,1, not 1.1. There should be some JS float filtering as it is on server side.
$form->addText('float', "Float")
->setRequired()
->setDefaultValue(1.1)
->addRule($form::FLOAT) // filters 1,1 to 1.1 only on server side
->addRule($form::RANGE, "%label must be at least %d", array(1.1, NULL)); // fails
// also EQUAL fails
Tested on stable 2.1.1.