level 20means that you want to download all pages that fit into the domain defined by the commands include anc exclude and can be reached from any of the start pages with no more that twenty link (mouse clicks).
You can also say
level inf
not to limit the mirrorring by the deepness. However using level inf
you should be certain that the download process is well coordinated by the
domain patterns, the command size, your physicall disc size or
network bandwith.
Use level inf only if you know what you are doing. During test we ended up downloading a costly 100 meg during a night. TOC