regexp: exclude repeated characters for highlight - hi-lock-mode

Question

I want to search using regexp to capture plain text. I want to capture passages that begin with opening quotation marks and end at the end of the paragraph, and even though the quote continues onto a new paragraph, I want to capture only the first part (In the following: The dog wagged it's tail.) Note that there are no closing quotation marks at the end of the paragraph because the quote itself continues.

Bob said: ``The dog wagged it's tail.

``But that's not the end of my story,'' said Bob, continuing.

I say I want to "exclude repeated characters" because I don't want to capture to the end of the paragraph when the quote closes, i.e., when there are closing quotes, thus:

''

In other words, I want to accept single apostrophes but not double apostrophes.

Edit: Now that I have this solution, provided by phils below, here's the complete result:

And once the file is loaded, enable hi-lock: M-x hi-lock-mode

Also: M-x customize-group RET hi-lock-faces

Answer 1

Based on the screenshot, you are only interested in quotes spanning multiple lines. Here's a patten for that:

"\\(``\\(?:[^'\n]\\|'[^'\n]\\)*'?\\)\n\\(?:.\\|\n\\)*?''"

Or in rx syntax:

(rx (seq (group "``" (zero-or-more (or (not (in "\n'"))
                                       (seq "'" (not (in "\n'")))))
                (zero-or-one "'"))
         "\n" (minimal-match (zero-or-more anything)) "''"))

---

Note that we handle single ' characters with this:

"\\(?:[^'\n]\\|'[^'\n]\\)*'?

Which says match zero-or-more repetitions of:

1. Any single character which is neither ' nor a newline.
2. A ' character followed by any single character which is neither ' nor a newline.

Followed optionally by a single ' immediately before the newline.

---

Group 1 is the part to highlight. e.g. with hi-lock-mode:

Hi-lock: (("\\(``\\(?:[^'\n]\\|'[^'\n]\\)*'?\\)\n\\(?:.\\|\n\\)*?''"
           (1 (quote hi-green-b) prepend)))