(The difference between psr-0 and psr-4 in composer) and (the difference between psr-0 specifications and psr-4 specifications) is not the same?

As the question, I am engaged in a little mixed, who can be careful to talk about: 1, composer psr-0 and psr-4 In the difference; 2, psr-0 specifications and psr-4 specifications of the difference; 3. composer and php-fig. For example, I am a bit confused. Who can tell me carefully:
1. The difference between psr-0 and psr-4 in composer;
2. Differences between psr-0 specifications and psr-4 specifications;
3. composer and php-fig.

Reply content:

For example, I am a bit confused. Who can tell me carefully:
1. The difference between psr-0 and psr-4 in composer;
2. Differences between psr-0 specifications and psr-4 specifications;
3. composer and php-fig.

In fact, it is a naming convention and automatic loading (autoload) a standard, specific can look at the PHP-FIG's official home page, there are detailed provisions and Examples

The psr-0 and psr-4 in composer doesn't mean the two norms, not because they are different in composer .. Composer can be understood as CentOS's yum, similar to the brew of Mac. composer is a PHP dependency management tool. For details about the automatic loading mechanism of composer, refer to my column: automatic loading of composer from Laravel study notes. I hope this will help you.