The visibility of this variable is public in the parent class. The overwitten visibility caused the following errors:
PHP Fatal error:  Access level to CRM_Admin_Form_Resource:: must be public (as in class CRM_Admin_Form)

It bumps the underscore version from 1.5.0 to 1.13.1

The backbone stack is deprecated in the civicrm. In the 5.37.1 version the libs seems to be missing (404 in browser console), so that the
Booking frontend application is broken.
Versions:
- Backbone: 1.4.0 has been added (developer version). I don't know which version was used in the civi.
- Marionette: 4.1.2 has been added (latest version). I think an older (<3) version was used in the civi.
- Modelbinder: 1.1.1 has been added (latest version). I don't know which version was used in the civi.

It is included from the civi backbone packages directory, so that is could be missing also.

Also use the LONG_NAME variable instead of the hardcoded module name

In the browser console the following error appeared:
Uncaught TypeError: Cannot read property 'Model' of undefined
Solution: If the Backbone is undefined, fallback to the window.Backbone.

The Backbone.Marionette is undefined in the current lib. But Marionette is defined, so it could be used instead.

As the Marionette.Module is deprecated and has been removed from the codebase, the utils.js triggered js error.
The utils.js function has been removed and the add-sub-resource app has been extended with the removed logic.

Console errors are not visible on the screen.
Changes:
- entites.js module elimination. The content has been added to the app.js.
- addInitializer has been removed, the onStart function has to be used instead
- move ResourceTableView from views to app as the modules are not supported

modules are deprecated and has been removed from the codebase

Use CRM.$ instead of $, and CRM._ instead of _

On the page header regions they were loaded later than the template finder function excution.
The missing template caused empty content.

Also fix the form selector

As the app.js is getting too long, some of the objects could be moved to separate files.
It helps me understanding the current issues.

As both modal trigger events the handler supposed to be the parent class

To be honest i don't know that it works well or not. Couldn't catch the render dialog event

It is handled with a function in common.js that is already loaded on the form

The current upgrader processes the xml files that has this suffix

Based on the solution that this fork applied: https://github.com/mjwconsult/civibooking

civix generate:entity-boilerplate

to resolve Unknown db error during extension install