What is the admsi.pl utility that is used during EBS patching?

Thanks to the blog post by Atul Kumar for explain this.
It's a tool for generating instance-specific patch installation instructions.

This tool was refered to in the beginning of a readme-file for a particular patch. The readme-file stated:

Instructions For Applying This Patch
Execute the following command to generate your instance specific installation instructions Source the Applications environment file Run the Patch Application Assistant by entering "admsi.pl".

A bit further down in the same readme-file:

Apply The Patch

For 12.0.X / 12.1.X / pre-upgrade patches (using adpatch), you must shut down all Application tier services before performing the tasks in this section. For 12.2.X patches (using adop), you can perform the tasks in this section without shutting down the Application tier services. Apply patch [required] This patch contains the following unified driver file to be applied with AutoPatch: u28389569.drv (This is the unified driver)

$ perl $AD_TOP/bin/admsi.pl -patch_top=/software/EBS/28389569
Gathering Information..
Enter the APPS user password:
Logfile for this session is located at admsi.log
Generating installation instructions for patch 28389569..
Updating database....
install_28389569.html generated successfully
install_28389569.txt generated successfully

The generated files will contain the exact patching instructions.