This is usually the step before proofreading.
On a basic level, the writing is assessed for correct and consistent spelling, punctuation and grammar. While on a more complex level, we dive into factual and stylistic consistency, flow, presentation of ideas in clear and logical forms, and whether the language and approach are suitable for the target audience – this is crucial and one of the areas where my journalistic experience can be very useful. By its nature, this type of copyediting incorporates what's sometimes referred to as line editing.
There are various rules in writing, but there are many subjective areas when it comes to the English language and how we present it. And, of course, there is the whole issue of which English variation you want to use. I work with British and American English (this website is written in British English, in case you're wondering).
A skilled copyeditor will be sensitive to each writer's voice and message, and they'll work closely with the writer to preserve their unique style – while also ensuring the words are being conveyed in a way that is smooth, easy to understand and, of course, professional.