Levels of Editing

Light Edit

A light edit should be performed on a manuscript that is relatively error-free: that is, well organized, clear, consistent, grammatical, and conformant with the publisher's style guidelines. Editors should

Review basic spelling, grammar, and punctuation, with reference to the publisher's style guidelines, correcting the manuscript using standard editors' marks.
Keymark the text (identify typographic elements using standard codes).
Mark callouts to figures, tables, and other floating display material.
Check for correct numeric sequence of heads, figures, tables, and other numbered elements.
Eliminate cross-references to physical positions of material (such as 'above' or 'below' on a page) if the client desires. This is becoming less of a concern, however.
Mark callouts for IPRs (references to a page in the book by its number).

An editor performing a light edit should not

Overhaul otherwise grammatically tolerable sentences to remove ambiguities or improve clarity, concision, or felicity of style.
Move material farther than an adjacent sentence to correct clarity or logical flow of presentation.
Add material to bridge gaps in logical flow.
Revise the head structure.
Research the accuracy of statements of fact.

The author may be queried on these matters if the editor believes it necessary to make the manuscript minimally acceptable (including corrections of fact if the editor can make the correction without performing research), but such querying should be very infrequent. If the 'light' editing tasks result in extensive markup or author querying, the editor should transmit a report to management describing the problems and quoting the most objectionable passages so that PS can negotiate for the authority and compensation required by the additional work. Negotiation may, unfortunately, result in the editor being instructed to ignore even glaring faults.

Medium Edit

A medium edit should be performed on a manuscript of average quality. A medium edit includes the tasks previously enumerated for a light edit, but markup due to those tasks is likely to be much more extensive. In addition, editors should

Reorganize and reword sentences to correct misleading or confusing sentence structure, querying the author as necessary.
Recast sentences to eliminate the use of third-person singular pronouns for subjects of unspecified gender, without impairing the clarity and flow of the text.
Enforce finer points of English usage, such as (but not limited to) the following:

(restrictive) 'that' vs. (nonrestrictive/appositive) 'which'
'while' (temporal) vs. 'whereas' or 'although' (logical contrast)
'because' (causal) vs. 'since' (temporal)

Ensure that heads govern sections that span the whole region of text (chapter or section) in which they occur, that the sections do not overlap, and that no head has only a single subhead on the level below it. Add, delete, or move heads if necessary, usually with author query.
Ensure that all works cited in text are listed in the bibliography or references, that all listed bibliographic items are cited in text, that all references conform to publisher's style, and that citations are correctly updated to reflect changes.
Maintain a style sheet that incorporates publisher's style requirements and includes all terms for which editor has had to make a style decision.
If required by client to do so, track permission status of all material (figures, tables, text) that has been taken from other works, and query author as to whether permission has been obtained.
Examine art to verify that each figure or table agrees with its description in text.
In a computer book, identify program and file names, user input strings, and program output by use of one or more special fonts, as required by the client's specifications.
Query author as necessary on any of these items and on factual errors and inconsistencies within the text.

In a truly medium edit, errors requiring correction as a result of these additional tasks should not be very frequent. Furthermore, an editor performing a medium edit should not

Extensively rewrite otherwise grammatical and logical sentences merely to reduce verbosity or increase vividness.
Move material farther than an adjacent paragraph to correct clarity or logical flow of presentation.
Add material to bridge gaps in logical flow.
Research the accuracy of statements of fact.

The author may be queried on these matters if the editor believes it necessary (including corrections on fact if the editor can make the correction without performing research). If the light and medium editing tasks result in excessive markup or queries, the editor should transmit a report to management describing the problems and quoting the most objectionable passages so that PS can negotiate for the authority and compensation required by the additional work.

Heavy Edit

Briefly, a heavy edit is any edit that goes beyond the bounds of a medium edit. Many different characteristics can contribute to making a heavy edit necessary, including the following:

Inconsistent spelling, grammar, and style, as can sometimes result from having multiple authors contributing material to the book or authors who are not native speakers of English
Authors consistently following styles that are widely at variance with the publisher's style guidelines (in which case PS can sometimes negotiate with the publisher for permission to follow the author's style)
Severe disorganization in presentation of topics; for example:

A topic not presented until several pages after it has already been invoked in the discussion of another topic
A topic introduced and explained several times over as if it were a completely new concept
A topic omitted that is necessary to link other topics together

Very frequent errors requiring correction in the course of the tasks in a light or medium edit
Misstatements or dubious statements of fact that require the editor to perform research to ascertain the truth of the situation
Writing that requires considerable puzzle-solving effort on the part of the editor to understand the author's point (perhaps because of poor organization or because of excessive use of jargon)
Extensive author markup of manuscript in poorly legible handwriting
Material whose length must be reduced to conform to publisher's requirements without omitting any points
Inconsistencies resulting from disruptions in the publisher's management of the project

In addition, a book that, because of its size and tight schedule, requires the collaboration of multiple editors requires heavy attention on the part of the sponsoring editor, whose duty is to maintain consistency between the portions handled by the different editors.

On a heavy edit, editors should mark and query manuscript, as well as develop and maintain auxiliary documentation, as needed to ensure the success of the edit. The editor may also perform a moderate amount of research to clarify or correct statements of fact (with author query to confirm the changes).

Nevertheless, the editor must take special care to keep track of editing productivity, with an eye to the budget allowed. If the editing work on a project is likely to exceed the budget, the editor must make sure that management is informed of the situation in a timely manner, and the editor may have to scale back the editing objectives.

Furthermore, even on a heavy edit the editor should refrain from making changes just for the sake of making changes or replacing the author's style by the editor's.