qr function elementary reflectors

Can some one tell me the type of the transformation (Householder or Gram Schmidt) used by the matlab function qr.

If The answers is Householder, then the mathematical form of the elementary reflector used by qr decomposition is: F = I - 2 (uu')/(u'u). " ' ": transpose operator and I: identity matrix.

What is the mathematical form of u used by the matlab function qr.