http://www.macdevcenter.com/pub/a/mac/2003/10/21/startup.html?page=last&x-maxdepth=0

StartupParameters.plist:

{
  Description     = "Apache web server";
  Provides        = ("Web Server");
  Requires        = ("DirectoryServices");
  Uses            = ("Disks", "NFS", "Network Time");
  OrderPreference = "None";
}

"Provides" specifies the services that this StartupItems provides. Provides can
contain multiple services, but it is not recommended. Here Apache provides a
"Web Server" service.

"Requires" specifies the services that have to be started before this
StartupItem is loaded. The values in this field are those of other
StartupItems' "Provides" fields. Apache requires "DirectoryServices" to be
loaded before it can be run; if DirectoryServices are not specified to run or
fail to run properly Apache won't run.

"Uses" specifics the services that should be started before this StartupItem is
loaded. This is similar to the "Requires" attribute except this service will
always be loaded, but only after it has tried to execute all the services in
"Uses". Apache uses the "Disks", "NFS", and "Network Time" services. OS X will
try to load these services, if it can't it will still load Apache, but only
after trying these services first. 

"OrderPreference" specifies the general time period in which a StartupItem will
be executed. This order is less significant than both "Requires" and "Uses" but
is used to determine order after evaluating those attributes. The possible
values for this attribute are: First, Early, None (default), Late, Last. Apache
specifies no OrderPreference as to when it should be loaded.