Hyphens, En Dashes, Em Dashes

Q. Can Chicago please provide clarification on hyphenation when “high school” is used as an adjective? For instance, do you prefer “middle and high school students” or “middle- and high-school students”? Why? One never sees “high-school curriculum” or “high-school classroom” in educational writing, but I don’t fully understand how the rules are applied toward permanent compounds used as adjectives in CMOS. Thank you!

Q. Lately I see more and more hyphenated -ly phrases, especially in digital communication—e.g., “a hastily-made decision.” Is this just my cognitive bias inventing a trend that isn’t there, or have your editors noticed more -ly hyphens as well? I know they’re more unnecessary than incorrect, so am I being fussy to mark them for deletion if they’re used consistently and doing no real harm to reader comprehension? Thanks as always for your insight.

Q. In a recent Q&A the hyphens look like en dashes to me. Are they, and if they are, why?

Q. I have an ongoing disagreement with another scholar that I’m hoping you can help resolve. He suggests that the phrase “early modern” requires hyphenation when used as an adjective (ex.: “early-modern literature”). I would instead say “early modern literature”; is there a right answer here?

Q. Is it “ice-cream sandwich” or “ice cream sandwich”?

Q. Can an em dash be used to connect two complete sentences? For example: “You don’t need to go to the DMV in person to renew your driver’s license—you can renew it online.” Thank you in advance for your answer!

Q. Our typesetter applied Chicago’s never-add-a-hyphen-to-a-URL-breaking-over-two-lines rule to hashtags breaking over two lines (specifically “#MeToo”), and the proofreader marked to force them all to one line, which may result in a lot of loose/tight lines since this occurs quite frequently. Would you suggest stetting the original, going with the proofreader’s fix, or hyphenating?

Q. Do you hyphenate “student teacher”?

Q. Does the Manual defend “on a case-by-case basis” over “case by case”?

Q. I know that the CMOS preference is not to hyphenate “noun + gerund” compounds, but in the case of “decision-making,” which appears with the hyphen in many dictionaries, would CMOS call for a hyphen? Thank you in advance!