Script Editors work with producers and writers as a script progresses to track its progress, ensure the story unfolds as initially agreed, and results in a captivating, moving outline for the film.
While it is a role requiring creativity and an understanding of the creative process, a script editor is there primarily to provide guidance for the writer.
They may make suggestions on things to change and ideas they have to solve problems but their overall concern is to ensure the vision of the writer (and possibly producer) is fulfilled as strongly as possible, not to drive the story with their own ideas.
Script editors usually work up through development or come from similarly creative editorial roles in other media such as theatre. This is also a frequent step in the road towards producing, though production experience is also an asset in that instance; producers must also be prepared for the practicalities of shooting. Feedback for the writer will be overseen by the script editor, building up a relationship to help them judge how best to provide notes on the script and which areas to leave alone when they suspect the writer will iron them out independently over a process of drafts.
Other notes on the script may come from development executives from companies providing funding for the film. When several different companies are involved this can lead to a wealth of responses, sometimes contradictory. This also goes some way to explaining why the process can take so long – the script will only progress once all concerned parties are happy with it.