  We present a formula for the regular part of a sectorial form that represents
a general linear second-order differential expression that may include
lower-order terms. The formula is given in terms of the original coefficients.
It shows that the regular part is again a differential sectorial form and
allows to characterise when also the singular part is sectorial. While this
generalises earlier results on pure second-order differential expressions, it
also shows that lower-order terms truly introduce new behaviour.
