I am proofreading a text, and I would like to change all occurrences of ' to the relevant character, ‘ or ’; ditto per " and double quotes. The task cannot be automated, because there are apostrophes in the middle of the text, like in "I'm", and of course " is heavily used in the XHTML markup. At the moment I am using Sigil, but replacing every single character takes a bit of time because of the tidying involved. Do you know of any better way?