Manuscript amendments are necessarily rare, but yesterday saw what looked like a textbook example of one.
That was the attempt to insert into the proposed ban on MPs' paid directorships and consultancies, a ban on MPs' working as paid trade union officials.
In point of fact, no MP is a paid trade union official. On that one, David Cameron is living in the fairly distant past.
But the Speaker refused to accept a manuscript amendment by the proposer in order to give the Prime Minister his stated price for his support.