Guide to Punctuation

extracted from http://www.informatics.sussex.ac.uk/department/docs/punctuation/node00.html

Introduction

The document you are looking at is a textbook, and it is written for people who find punctuation difficult. If you're not too sure where commas ought to go, if you're puzzled by colons and semicolons, if hyphens and apostrophes are something of a mystery to you, then this document is for you.
The document starts at the beginning and assumes no knowledge of punctuation at all. Each punctuation mark is introduced in turn; its proper use is described with the aid of lots of examples; wherever possible I give you some simple rules for checking your punctuation.
The space devoted to each punctuation mark reflects the degree of difficulty that most people have with it. For example, apostrophes and bracketing commas, which between them probably account for about half of all punctuation mistakes, receive a great deal of discussion, while question marks are dealt with much more briefly, since hardly anybody finds them difficult.
A notable feature of the document is its inclusion of many examples which are badly punctuated. These are always marked with an asterisk (*), and the text explains in each case what is wrong. All of the most frequent punctuation mistakes are treated in this way.
The punctuation described here is the style which is currently the norm in Britain and the Commonwealth. Standard American usage differs in a few respects; in these cases, American usage is also described, but examples of specifically American punctuation are always marked as follows: (A). If you are writing expressly for an American audience, you should follow the American norms.
The document also covers a few topics which are not strictly aspects pf punctuation, such as the proper use of capital letters, of contractions and abbreviations and of diacritics. The document concludes by explaining the proper way to handle titles, footnotes, references and bibliographies, and it also covers the punctuation of personal and business letters.
Since many people these days do most of their writing at a keyboard, and especially with a word processor, this document also explains the proper use of italics, boldface, small capitals and the special characters available on a word processor.
Acknowledgements
I am indebted to Lisa Wale, Max Wheeler, Richard Coates, Margaret Crowther and an anonymous reader for their valuable comments on earlier drafts of this document, and to Lisa Wale for providing many of the examples. Any remaining shortcomings are my own responsibility.