keras/src/regularizers/regularizers.py/L1L2/__call__
class L1L2:    def __call__(self, x):
        regularization = ops.convert_to_tensor(0.0, dtype=x.dtype)
        if self.l1:
            regularization += self.l1 * ops.sum(ops.absolute(x))
        if self.l2:
            regularization += self.l2 * ops.sum(ops.square(x))
        return regularization