Or, This is Not a Guide to Proper Punctuation.

Because where punctuation is concerned, the dirty little secret is that most of the rules are a lot more like local customs.  Different languages have different customary punctuation, and so do different time periods.  Medieval English texts had next to no punctuation at all — once in a while, if the text was meant to be sung or chanted, the scribe might throw in a mark that would someday be a comma or an apostrophe, as a way of saying to the reader, “take a breath here; you’re going to need it.”

Modern editions of older texts — especially the renaissance and medieval stuff — often impose modern punctuation on the material, in the interest of making it more accessible to the reader.  Standardized, or at least sort of standardized, punctuation came in with printing, and it was the printers, not the writers or the readers, who more-or-less codified it.

Even today, there’s a lot more leeway in the area of punctuation than your old high-school grammar texts would have had you believe.  Sure, sentences need to end with a period or a question mark or an exclamation point, and using a comma splice instead of a semicolon is just plain wrong, but when it comes to things like whether to use a colon or a dash, or paired dashes instead of parentheses, or serial-comma-yes versus serial-comma-no . . . you’re on your own.

And don’t worry too much.  You can get away with almost anything, so long as you’re consistent about it.

(Get your dialogue punctuation right, though.  It’s all purely arbitrary, done according to conventional rules that are easy enough to learn and to follow, and to check for errors in the final draft.  And messing them up is likely to put off a potential reader faster than almost anything.)