Not sure what you mean by "example". We both know what the rule *is intended to say*, but it doesn't *actually say* so. An improvement would be:

> The autoloader MUST convert each namespace separator to a `DIRECTORY_SEPARATOR` when loading from the file system.

But what if the autoloader caches the mapping? Then it will do the conversion in advance and check the mapping when loading. So we can further improve it:

> The autoloader MUST convert each namespace separator to a `DIRECTORY_SEPARATOR`.

But then the rule doesn't say what it applies to ("each namespace separator where?") and what the result is. So we can further refine it to:

> The autoloader MUST turn fully qualified class names into file system paths by replacing the namespace prefix with the corresponding base directory, replacing each namespace separator with a `DIRECTORY_SEPARATOR` and appending `.php` to the result.

Better. Now then the question is: How does the autoloader find the corresponding base directory? What if there are many?

This goes on.

To shorten my point: Many of the rules in this proposal have flaws like these. The inherent problem is that we are describing the *algorithm* that should be implemented by an autoloader. What if an autoloader uses a different algorithm but produces the same results (file system paths) for the same inputs (FQCNs)? It won't be considered compliant.

That's why I turned the perspective of the proposal. I changed the rules to describe a *relationship* ("correspondence") between namespaces and directories. How the autoloader establishes the relationship, whether it uses caching or any other fancy tricks, is secondary.