version of the legislation是什么意思?

version of the legislation是什么意思?
原句如下:
President Bush met with Senate Republicans at the US capital Thursday ahead of expected Senate passage of a bill dealing with the treatment and trials of terrorism suspects.Mr Bush says the measure would give him an important tool in the war on terrorism.
A day after the House of Representatives approved his version of the legislation,President Bush urged the Senate to do like wise.
我知道是"立法的版本",可关键是什么叫"版本"呢？布什又不是写书的，立法还有版本?
他在这里让众议院和参议院通过了一项立法，为什么说成是“立法的版本”呢？可以说是“立法的文件”或者“立法的条款”啊！