Notice 90-20 is the 20th Notice issued during 1990, and it appears on page 328 of Volume 1 of the Cumulative Bulletin in 1990.
Reg. Section 1 is the type of regulation. 163 is the related code section. -10 is the regulation number. (a) is the regulation paragraph. (2) is the regulation subparagraph.
a. This is a Temporary Regulation; 1 refers to the type of Regulation (i.e., income tax), 956 is the related Code section number, 2 is the Regulation section number, and T refers to temporary.