These are four levels along a continuum, with proofreading involving the least amount of work and rewriting involving the most. Proofreading is intended to catch mistakes in spelling and formatting. Editing goes a step further and may involve word choice consideration, for example, and correction of grammatical errors. Revision calls for significant shifting of sentences and perhaps inclusion of some new content. Rewriting involves striking entire sentences and paragraphs, major juggling and deletion of existing content and introduction of entirely new content.