Single-Sense Rule

The Single-Sense Rule is the rendering half of the Zero Information Casualty standard:

No information may be locked behind a single sense.

Every rendering requirement in ZIC follows from it, and anything that doesn't follow from it doesn't belong. It is the Tyrer Doctrine applied to a web page.

Information, not decoration

The rule is about information, and "has nothing whatsoever to say about beauty."

• Colour is fine. Colour as the only carrier of a status, category or warning is not. "Use whatever colour you like. Say it in words as well."
• An image is fine. An image carrying information available nowhere else is "a locked room".
• A typeface is fine. Emphasis carried only by a typeface is not, because italic doesn't survive the journey.
• Position is fine. Meaning carried only by position is not.
• Size is fine. A heading that is only large "is a heading to one sense and a paragraph to every other".

The test

For any element: is there information here that exists in one sensory channel and nowhere else? Put another way: if it were removed entirely, would any information be lost? If yes, it must also exist in the semantic layer. If no, it is decoration, "and none of this specification's business." A conformant site may be as rich and branded as its publisher likes. "It may not keep a single fact where only one sense can reach it."

Its companion of equal rank is the Position Principle.

Behind the scenes

A real idea, from Zero Information Casualty v1.7, the design standard by Charli-Jo Tyrer and Claude, §1.11, §2.2 and §2.4. This entry summarises it; the standard is the authority.