What is this side panel called in the documentation page?

[macMonkey]

I want to replicate the look of the side panel that pops up when you click mass update. I tried searching side panel in the documentation but it was something...

[macMonkey]

According to the file structure in the picture, how can i refer “distributeLeadshandler.js” as the handler in the “Leads.json” code:

{

...

[macMonkey]

this my file sttructure from the src file inside the ext-template repo which i cloned and modified:
.
├── files
│ ├──...

[macMonkey]

I've read the official development documentation(partialy) and also fully read the information on the ext-template repo. Is there any site on web where...