The subtraction of two identifiers is now permitted as part of a constant expression. An optional expression can follow the symbolic difference. The expression is limited to addition, subtraction, multiplication, and division binary operators. The normal expression evaluation rules have been altered a bit such that the symbolic difference is assumed to be contained within parentheses. The expression following the binary operator can be any legal constant expression.
foo:
.quad bar - foo * 2 # The result here is 16.
bar: