sentences:  Cleanroom software engineering is another approach, which requires the team to work from an exhaustive written specification of the software's functionality, without access to its code.Netscape's project to improve HTML layout in Navigator 4 has been cited as an example of a failed rewrite.The new layout engine (Gecko) had developed independently from Navigator and did not integrate readily with Navigator's code; hence Navigator itself was rewritten around the new engine, breaking many existing features and delaying release by several months.