Codimension-two extension of regular functions on a normal variety ($\Gamma (X,{\mathcal{O}}_X)\cong \Gamma (X\setminus Z,{\mathcal{O}}_X)$)

For an integral normal variety that is Noetherian, removing a closed subset of codimension at least two does not create new regular functions. Affine-locally, a normal Noetherian domain is the intersection of its localizations at height-one primes inside its fraction field. The complement still contains every height-one point, so a regular function on it lies in each such localization and therefore in the original ring. On projective space this also follows directly by excluding irreducible polynomial factor of the denominators on each polynomial affine chart.