What are the custom blocks icon in the editor?

[LeonexSMBX1]

Hi everyone, I was scrolling through the editor, and then I came across some weird blocks and BGOs. There like 300 of them, and they are just titled ''custom block" or "custom BGO", I couldn't find any information about them on the forums, YouTube, or even the manual. Does anyone have any idea what are they for, and how do I use them? I suppose they are there to use instead of replacing already existing blocks, can anybody help me?

[Emral]

https://docs.google.com/document/d/1sID ... m2zj9ak602

[LeonexSMBX1]

Umm... I can't access the file...

[Emral]

Umm... I can't access the file...

Oh, oops! Linked the wrong one.
https://docs.google.com/document/d/1uOd ... m2zj9ak602

[LeonexSMBX1]

Thank you Enji for your reply, I needed that.