A committee might call for public hearings on important bills. Each committee is led by a chair who belongs to the majority party and a ranking member of the minority party. Witnesses and experts can present their case for or against a bill. Then, a bill may go to what is called a mark-up session, where committee members debate the bill's merits and may offer amendments or revisions. Committees may also amend the bill, but the full house holds the power to accept or reject committee amendments. After debate, the committee votes whether it wishes to report the measure to the full house. If a bill is tabled then it is rejected. If amendments are extensive, sometimes a new bill with amendments built in will be submitted as a so-called clean bill with a new number. Both houses have procedures under which committees can be bypassed or overruled but they are rarely used. Generally, members who have been in Congress longer have greater seniority and therefore greater power. A bill which reaches the floor of the full house can be simple or complex and begins with an enacting formula such as "Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled..." Consideration of a bill requires, itself, a rule which is a simple resolution specifying the particulars of debatetime limits, possibility of further amendments, and such. Each side has equal time and members can yield to other members who wish to speak. Sometimes opponents seek to recommit a bill which means to change part of it. Generally, discussion requires a quorum, usually half of the total number of representatives, before discussion can begin, although there are exceptions. The house may debate and amend the bill; the precise procedures used by the House and Senate differ. A final vote on the bill follows. Once a bill is approved by one house, it is sent to the other which may pass, reject, or amend it. For the bill to become law, both houses must agree to identical versions of the bill. If the second house amends the bill, then the differences between the two versions must be reconciled in a conference committee, an ad hoc committee that includes senators and representatives sometimes by using a reconciliation process to limit budget bills. Both houses use a budget enforcement mechanism informally known as pay-as-you-go or