What is the difference between entries in Pug?

Question

css

What is the difference, why is it done that way that you can write using Pug
and so div.main-block
and so div(class="main-block")

Answer 1

And besides class, there are no attributes, or what?

div(class="main-block", id="sdas", data-prop="value")

Answer 2

- var className = 'block--red'
div(class="block "+className)

Answer 3

A class is usually not written like this, this is for other attributes. For a class, this is convenient if you need to substitute a variable in the class.