Grep, Italicise Quotes

I'm trying to italicise the contents of quotes within my document (am happy for the quotes to also be made italic, so no worries about being too clever trying to exclude them)

That's actually fairly easy -- apart from one tiny little issue

The usual way to delimit some string without including the delimiters is to use Lookbehind (?<=xx) before and Lookahead (?=yy) after the string. A typical example is

(?<=\().+?(?=\))

to find everything between parentheses, excluding the parentheses themselves (the open and close parentheses have to be escaped because they are 'special' inside the lookbehind/lookaheads). Similar to your previous query, it needs a shortest possible match to prevent grabbing an entire paragraph when possible.

So you would think all that's needed to exclude your quotes from the string is this expression:

(?<=").+?(?=")

Not ... exactly. This seems to match all strings with a double quote on its left and right, but InDesign does something unexpected:

It matches both each opening and closing (curly) quote with the single character ", so everything between the 'between the quotes' also matches! The only thing you can do to prevent this (not really the only thing, actually) is to explicitly check for a double opening and a double closing curly quote, like this:

(?<=~{).+?(?=~})