Craft 3: multisite and assets I am a little bit confused by the documentation about assets. It says that paths are relatives from the directory that holds the index.php file. 

Now, I am working on multisite, with the following folders:
    craft/web/site1/
    craft/web/site2/  

Is it possible to have:
    craft/assets/site1/
    craft/assets/site2/  

Or:
    craft/web/site1/assets/
    craft/web/site2/assets/
Your second example is easy enough... just make sure the assets folder exists under both of the site1 and site2 folders, the under your Asset Volume settings in the Control Panel, set the "File System Path" to the relative assets.