Back when I worked for Congress, 1982-90, tax legislation — or negotiations in Congressional Conference Committee — often started with what staff called “underbrush” — pieces of a bill that everyone could agree on. “Everyone” meant six or seven groups: majority and minority staffs of Ways and Means in the House and Finance in the Senate (that’s four), Joint Tax Committee staff (that’s five), and the Executive Branch, maybe Treasury and the IRS (that’s seven) or maybe Treasury spoke for the IRS (that’s just six).
Underbrush, as I recall, tended to start with technical corrections to the most recent big bill. Underbrush expanded to include corrections to older bills, then to tax provisions that for whatever reason were noncontroversial. As the Senate and House negotiated, Joint Tax staff would print spreadsheets listing provisions each side proposed. When each side had identical provisions, those provisions, both corrections to old legislation and New Starters, usually became underbrush — agreed as part of the new package, and not needing further negotiation. Usually, but not always.