SQL 2012 - Can we access or Modify SSIS XML in SSIDB database?

Hi, 

So in SQL 2012, all packages are maintained in the "SSISDB Catalog".  SSISDB is the also the default database created in relation to this (when we create a catalog).

I have a few queries - 

1) Is the package stored as an XML in an XML datatype column in a table in SSISDB database ?

I see that the "package_data" in internal.Packages table is NULL , so it's not the same as it used to be before in SysSSISPackages.

OR 

         2) Is the package stored Physically as an XML file somewhere ?

So in other words, how does the CATALOG store the package ?

Also, what about the SysSSISpackages table in MSDB , is that not relavent anymore ?

I can see none of the packages deployed to the Catalog, have anything to do with having a reference in the SysSSISpackages table - as was the case in the past.

Please clarify, Thank You.

P