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 engine’s apostrophe rule handles the word-internal case and the year; the quote rule then pairs what is left. The order matters: apostrophes must be claimed before quote-pairing sees them.

Feet and inches stay straight

In 5'10" the marks are measurements, not punctuation. The engine’s quote rules refuse to read a straight mark after a digit as a closing quote, 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: "It's 5'10", maybe," she said is a thicket, and «It’s 5'10", maybe,» she said reads at a glance — every mark now says what it is. Quotation marks pair up, apostrophes curl, measurements stay straight.

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.