3.12.5 All parts lying on the reference and step planes, in addition to the transition between the two planes, must produce uniform, solid, hard, continuous, rigid (no degree of freedom in relation to the body/chassis unit), impervious surfaces under all circumstances.
Forward of a line 450mm forward of the rear face of the cockpit entry template, fully enclosed holes are permitted in the surfaces lying on the reference and step planes provided no part of the car is visible through them when viewed from directly below. This does not apply to any parts of rear view mirrors which are visible, provided each of these areas does not exceed 12000mm² when projected to a horizontal plane above the car, or to any parts of the panels referred to in Article 15.4.7.
3.12.10 In an area lying 650mm or less from the car centre line, and from 450mm forward of the rear face of the cockpit entry template to 350mm forward of the rear wheel centre line, any intersection of any bodywork visible from beneath the car with a lateral or longitudinal vertical plane should form one continuous line which is visible from beneath the car
Enclosed holes are only explicitly allowed in the front of the floor, which implies they are prohibited elsewhere. RBR argued that they weren't explicitly banned from the 50cm outer section where they put them. The FIA issued a technical directive that clarified the rule, saying yes, this means holes are prohibited everywhere else. RBR was allowed to keep its results because the FIA thought their interpretation of the rule was fair prior to the clarification stating the clearer meaning of the regulation.
Car is legal as long as it isn't illegal and the floor was deemed illegal after Monaco.