Where do the limits of CMS capabilities end in comparison to web development?

Question

CMS

1. What are the most "top" CMS exist?
2. Where do their limits of possibilities end, compared to web development? What can not be done special on the CMS?
* By CMS I mean all kinds of web-constructors.

Answer 1

What are the top engines out there?
Where do the possibilities of engines end and the possibilities of other ways to move something begin?
You understand that it is impossible to say that there is the most top-end, because the question of the scope will immediately become.
Ride, fly, crawl, spin.
It is the same here - there are no "top" ones, there are popular ones for solving specific types of tasks.
Any CMS is usually a web product, and if desired, EVERYTHING can be implemented in a CMS, but sometimes the task is such that it makes no sense to rewrite the CMS, but it's easier to write your own from scratch.

Answer 2

What are the "top" CMS exist?

if we are talking about php, then what criteria do you need top ones for?
The most common is wp.
Nowhere. You can write anything within any system, since PHP is a scripting language in itself, nothing prevents you from getting into the code and breaking everything to write additional functionality. It just takes more movement. And a long incense of mana. For most of the functionality has already been implemented in its own way, it is necessary either to rewrite taking into account the many connections, or to write your own and fasten it to the existing system.