I think a lot of people have responded based on the topic and not read the extra text that mentions tags and syntax.
It's very much possible to know a large volume of tags and syntax. If you use the same language everyday in your job for example, much of it sticks. It becomes like learning a spoken language. After you've written or spelt out a word enough times you'll remember it. Similar words become easier to remember, just as similar syntax becomes easier to remember.
One way to learn syntax is to ensure you type out the code, even if your copying/utilising other code. Don't copy/paste.
I doubt you'll ever learn 'all' as you'll probably never use every one in a language.
Look. Sometimes when people are planning a project, something to consider is if your team know the technology to be used.
This serves to estimate the duration of the project and your cicles . The beginning cicles of the project can be used to learn.
In the end developers don't need to learn how to program again. Just need to learn the new tool.
Learn a new language can cost days, weeks or months. Learn programming ( Paradigms, Patterns, Protocols, ...) will always take years.
Definitely possible. People learn to write Chinese as well with their many thousand complicated symbols.
The key (along with regular practice) is well-planned repetition to transfer the short-term knowledge into long-term memory.
As long as you do that, you can just stack up. Brain's got a lot of memory.
Short answer is no, long answer is nooooooooooooooo.
Kidding aside, codes are just temporary tools in a programmers arsenal to solve a problem hence they need not to be remembered but the intuition behind the solution to a problem is the one going to be remembered hence a programmer may partially remember parts of the code by remembering what problem it solves.