A short, single-paragraph "elevator pitch" describing what the feature is.
Describe the problems that this proposal seeks to address. If the problem is that some common pattern is currently hard to express, show how one can currently get a similar effect and describe its drawbacks. If it's completely new functionality that cannot be emulated, explain why this new functionality would help Homebrew users.
Describe a solution to the problem. Provide examples and describe how they work. Show how your solution is better than current workarounds: is it cleaner, safer, or more efficient?
Describe the design of the solution in detail. The detail in this section should be sufficient for someone who is not one of the authors of this proposal to be able to reasonably implement the feature.
Describe alternative approaches to addressing the same problem and why you chose this approach instead.