Question

How many different block tags like these exist?

{% block %}

In other words if I have a parent template and child templates with multiple block tags. How does Django know where to insert if not by different block tag names?

Or can I customize like:

{% block_mytag_1 %}

Answer 1

Neither of these will work.

The documentation clearly explains this – you need to give each block in your parent template a different name:

{% block maincontent %}

This will be filled by whatever block in your child template has the same name.