iRules amatuer What does this iRule do?

when HTTP_REQUEST { 
   switch -glob [HTTP::uri] {
      "/onlineserv/HB" -
      "/beta/HB*" -
      "/preprod/HB*" {
          Lookup the host based on the HTTP host header
         log local0. "host = '[HTTP::host]'"

          Check if the host header exists and isn't an IP
         if {[string match -nocase {*[a-z]*} [HTTP::host]]}{
            set ibHost [class lookup [HTTP::host] USP_IB_REDIRECT_DG]

            if { $ibHost != "" } {
               log local0. "ibHost found: '$ibHost'"
               node $ibHost
            } else {
               log local0. "ibHost not found" 
               HTTP::respond 404
            }
         } else {
            SSL::disable serverside
         }
      }
      default {
          Default action is to use the VS default pool for non-matching URIs
      }
   }
}