The structure of an interaction design pattern

An interaction design pattern usually consists of the following elements:

• Problem: A Problem is related to the usage of the system and is relevant to the user or any other stakeholder that is interested in usability. 
• Use when: a situation (in terms of the tasks, the users and the context of use) giving rise to a usability problem. This element describes situations in which the problem occurs. 
• Principle: a pattern is usually based on one or more HCI principles such as user guidance, or consistency, or error management. 
• Solution: a proven solution to the problem. A solution describes only the core of the problem, and the designer has the freedom to implement it in many ways. Other patterns may be needed to solve sub-problems. 
• Why: How and why the pattern actually works, including an analysis of how it may affect certain attributes of usability. The rationale should provide a reasonable argument for the specified impact on usability when the pattern is applied. The why should describe which usability aspects should have been improved or which other aspects might suffer.
• Examples: Each example shows how the pattern has been successfully applied in a real life system. This is often accompanied by a screenshot and a short description. 
• Implementation: Some patterns provide implementation details.