What is the idea to accept both, file paths and URL as alias? I see this as big source of potential errors.
Wouldn’t it be safer to at least mark the two differently? Like @ for file paths and % (or something else) for URLs? Alternatively it could be made an convetion to add a Url as suffix for all URL aliases.
My biggest worry is, that the familiar @web alias now contains the base URL. @baseUrl would be much less confusing for poor yii2 veterans like me.