Explain in human language what is a web framework in php?

Question

PHP

Hi all! It's been more than a month since I've been hearing advice (switch to a framework). Before that, I wrote everything myself from scratch. You can't ignore that many and at least not deal with this thing. In connection with this, a few questions, what is it all about. Please do not give links to Wikipedia, etc. because I re-read everything there for a long time, but I didn’t really find anything sensible on my questions:
1. Will I be able to write my modules on the framework ( any and any complexity ) for my CMS. Surely not one framework does not have the function of analyzing its own content (for subsequent promotion) on the principle of search robots. Will the framework prevent me from creating such modules because of its limited functionality.
2. Will I be able to improve any module of the framework (for example, adding comments) to suit my needs without interfering with its update (if a new version is released). Or will I have to rewrite everything with the release of a new version, as I have to do on a CMS like DLE.
3. How much will I depend on the release of new versions? For example, I want to download now and then do anything with it without being afraid, as in the previous question, that they will find some kind of vulnerability and again have to update it and rewrite all my codes in hundreds of php files.
4. Will it be possible (excluding the option that I will copy the site to the local area and rewrite it from scratch to the framework for a year) gradually, without disrupting the operation of the site, transfer my own CMS to the framework, given that they have dozens of modules, their own admin panels and etc.
5. And finally, I chose, say, a framework. And the developer covered its further development. Can I leave the framework and continue to use it without rewriting all the files again to the new framework.
PS I apologize for the most likely strange questions, but before that I wrote everything myself, did not use any CMS (come with DLE for a very long time) or Frameworks, so I can not decide and start transferring all my projects to the framework.

Answer 1

Will I be able to write my own modules for my CMS on the framework

If your CMS is written in a framework - yes. Partial integration is also possible, but this is the path of pain.
A framework is a framework for building applications. He does not solve business problems, instead - technical ones.
It can interfere only if the principles adopted in the framework contradict the principles in your project. This is only possible if you explicitly chose the wrong framework. For example: to work with the database, you use Doctrine2 to the fullest, you choose the yii2 framework and partially switch to its ActiveRecord - this will lead to big problems.
Yes, fork the framework, publish the fork in composer and write whatever you want there. When updating the framework, you pour changes into your fork.
If you have a dependency in the composer only with the latest version of the framework - you yourself are an evil pinocchio)). Specify a fixed one and update as you wish, or don't update at all.
Dependence on new versions of the framework is entirely up to you. How to write and you will depend))
Simply put, you want the perfect code, this does not exist, take it as the original.
From a part and for this reason, it is also not customary to make any edits in dependencies, you only load them through the composer. Security updates - as a rule, these are minor versions that do not affect the API of the framework, so there should be no problems.
Yes
You can fork the framework and publish it to composer. True, such a situation is extremely rare for frameworks and rather signals that you have chosen a worthless framework.

Answer 2

In short: a framework is an ant farm for your code.
Yes, you will be able to write modules and develop the project after the framework stops developing.
I recommend Yii or Laravel.