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Characters and encoding


For Markdown source files use only UTF-8 encoding with no BOM (byte-order mark).

Prefer actual Unicode characters – which a modern text editor will display correctly – to both character entities and HTML character entities, which degrade the readability of the source. (HTML character entities are more readable than character entities, but different browsers support different subsets of them.) Thus, use π rather than Π or π.

  • Windows allows many characters to be typed as ASCII codes from the numeric keyboard, eg Alt+0215 for ×. (See the W3C list of HTML character entity references for codes.)
  • Mac OS X provides a graphical palette of Unicode characters.

If a character proves particularly difficult to source (for example, the romaji O-micron) try using its character entity, displaying the result in a browser, then copying and pasting the character from the browser back into the source. (A good idea in such cases to leave the character entity embedded as a comment.)

Use real ellipses (…) because three periods can be broken across lines or pages.

  • In Windows Alt+0133 on the numeric keypad
  • On Mac, Opt+;

Ligatures are typesetters’ tools for setting two letters together. Reserve æ for languages, such as Danish and Norwegian, in which it is a distinct character, not for words such as mediaeval.

Quotation and quote marks

quotation mark character usage
single typewriter quote ' only in code
double typewriter quote " only in code
typographers’ double quotes “” reported speech or verbatim quotation, titles of published articles
single typographer’s quote as apostrophe; to remove emphasis

Removing emphasis is the opposite of emphasis. The words de-emphasised are not to be understood as carrying their literal sense.

At the conference he said, “Today I’d like to talk to you about the ‘vision thing’ you’ve heard so much about.”

Do not use apostrophes to form plurals.

The possessive of a word ending in s is formed with a trailing apostrophe. For example:

Many MPs say that, unlike most MPs’ expenses, this MP’s expenses are questionable.

People in their 60s know “St James’ Infirmary Blues” was not 1967’s biggest hit, not even one of the 1960s’ biggest hits.

Acronyms, abbreviations and truncations

Set acronyms (pronounceable or not) in upper case without periods, e.g. IBM not I.B.M., HTTP not http.

Abbreviations are formed by omitting characters from the middle of a word, truncations by omitting characters from the end. Suffix a truncation with a period; not so with abbreviations. For example

  • Dr Kenneth E. Iverson
  • Mr & Mrs J. Smith
  • M. le President


Use the serial or ‘Oxford’ comma where necessary to avoid ambiguity.

The Oxford comma cannot safely be used without thought.

  • It can resolve ambiguity in a list.
  • It can introduce ambiguity into a list.
  • Some lists have ambiguities that its use or omission do not resolve. The ambiguity can be resolved only by rephrasing.

Wikipedia: Serial comma

Commas can have semantic force outside lists, e.g. Let’s eat, Grandma!

Hyphens and dashes

Hyphenate adjectival phrases, e.g. real-time systems do things in real time.

Use spaced endashes for parenthetical remarks – such as this one – but never hyphens or unspaced emdashes. (The longer emdash—like this—is the more common style in American typography.)


Use sparingly, not simply as a synonym for and, but to mark an association closer than conjunction.

Thus, Kernigan & Ritchie, and Proctor & Gamble, but authentication and access control.

Exception Wherean ampersand is part of a label on a UI control, reprosduce it faithfully.