One key, four characters: apostrophe, quote, inch, prime

The typewriter gave one key the work of four characters, and we still type it. A straight ' may be an apostrophe (don't), an opening or closing quotation mark ('no'), a foot mark (5'10"), or a prime (48°51′). The reader tells them apart without noticing. Software has only the surrounding characters to go on, and this is where most smart-quote implementations fail.

The apostrophe is not a quote

The right character for an apostrophe is ’ (U+2019) — the same character as the English closing single quote, which is the whole problem. It's is easy: a ' between letters is an apostrophe. The hard cases sit at word edges:

• '90s — the mark opens the word, but it is an apostrophe standing for the missing 19, so it must curl right: ’90s. A naive opener-by-position turns it into ‘90s, and you will find that bug in shipped word processors.
• Ukrainian п'ять — an apostrophe between a consonant and an iotated vowel, inside a word that a Latin-only test does not recognise as one.

The quote rule runs first, and it sets apostrophes aside before it pairs anything, so pairing never sees them: the word-internal case, the year and the elisions of the language pack. The apostrophe rule, second, then curls them.

Feet and inches stay straight

In 5'10" the marks are measurements, not punctuation. A straight " right after a digit never opens a quotation (it can still close one, as in "call 911"), so a 2" pipe and a 4" pipe keeps both inch marks rather than turning the text between them into a quotation. The known limits page lists the case that still goes wrong — an inch mark inside a quotation closes it early — because listing it beats guessing.

Strictly set text uses the prime ′ (U+2032) and double prime ″ (U+2033) for feet, inches, minutes and seconds: 5′10″, 48°51′24″. The engine does not set primes for you — deciding that a " is an inch and not a quote is already the hard part, and it errs on the side of leaving measurements exactly as typed.

What the right characters buy

Set side by side, the difference is not pedantry, and this example also shows where the engine stops. "It's 5'10", maybe," she said comes out as «It’s 5'10», maybe,» she said: the apostrophe curls and the foot mark stays, but the inch mark closes the quotation early. That is the known limit above. The workaround is to type the prime yourself: "It's 5′10″, maybe," she said becomes «It’s 5′10″, maybe,» she said, the engine leaves typed primes alone, and every mark now says what it is.

Try it

Paste The '90s called: it's a 5'10" frame, a 2" pipe and a 4" pipe. into the playground and check the Changes tab: the apostrophes curl, the foot and inch marks stay exactly as typed.

Something wrong or unclear here? Report an issue.