Punctuation
Apostrophes and Quotation Marks
Use the typographic characters (also called smart quotes) for apostrophes and quotation marks.
Note that in Firefox for desktop and Firefox for Android in en-US this rule is enforced programmatically so a developer’s code will be backed out if a text string contains the straight apostrophe or quote.
Commas
In the product, use serial commas (also called Oxford commas).
The success of the internet as a public resource depends upon interoperability, innovation, and decentralized participation worldwide.
Do
The success of the internet as a public resource depends upon interoperability, innovation and decentralized participation worldwide.
Don’t
Hyphens and Dashes
Use hyphens (-) to create a single idea out of two or more words. Don’t add a space before or after the hyphen.
Use en dashes (–) for ranges, like numbers (e.g., 1–9) and dates. Don’t add a space before of after the en dash.
Use em dashes (—) to set related — but separate — thoughts off from each other. Add a space on either side of the em dash.
Ellipses
Use with Button or Menu items when the action requires additional user input, usually via a Dialog, an Alert or moving the operation to another window or part of the UI.
Do not use an ellipsis in a link to indicate that more information is available at the destination.
In general, do not use ellipses in body copy.
Exclamation Points
Use sparingly, when the text reflects genuine excitement, not as a way to create excitement. Exclamation points aren’t a substitute for creating excitement.
Periods and Other Terminal Punctuation
Terminal punctuation signals the end of a text element. A period is the most common terminal punctuation. Use terminal punctuation at the end of a sentence in normal body copy. In general, do not use punctuation at the end of a headline, button label, checkbox or radio button label, tooltip, text link (unless the link ends a sentence), or navigation element.