Here is an idea that popped up in #236 and that builds on #232. When the root package configures this: ```json "extra": { "discovery": { "psr/http-factory-implementation": "My\\Psr17Factory" } } ``` then we shouldn't need auto-installing any extra packages for this virtual package. Same when listing individual interfaces: ```json "extra": { "discovery": { "Psr\\Http\\Client\\ClientInterface": "My\\Psr18Client" } } ``` In this case, we should verify that all the interfaces required to fulfill one of the supported `*-implementation` are listed.