There are private (service) blocks that help write a complex element. And how to distinguish them?

Question

BEM

How to understand that this block is private (service)? And that it was not made in order to use it separately elsewhere on the site. And to simplify writing a complex element?
I found about service blocks here:
https: //ru.bem.info/forum/149/
and here:
https: //github.com/bem-site/bem-forum-content-ru/issues/158
" An exception may be the situation when such an element has a too rich inner world and a desire arises to make its own elements. Then this can be presented as a service "private" block."

Answer 1

> How to understand that this block is private (service)?
You wrote it in its documentation/block comment/block name etc.
BEM doesn't care.
On the other hand, if the block itself fits some other situation, then this is a completely independent block and why not use it elsewhere ...