What do "Fix", "Fix N errors" and "Ignore" do in the Quality review?

From version 1.9.15, each error found by the proofread has a "Fix" button that replaces exactly the words that are wrong with the correction, and nothing else in the chapter, so a fix cannot introduce new mistakes. "Fix N errors" does that for every error of the chapter at once. The previous text is kept in Versions. When the wrong words occur more than once in the chapter, the button says "Fix in editor" and opens the editor on the passage, so that you choose the right place. "Ignore" dismisses a finding for good: it does not come back when you check again. Optional suggestions have "Apply" instead of "Fix" and never count as errors. "Polish chapter" is still there as a second step: it now works from the findings and leaves every correct sentence as it is.