Copying Text from Web Message Box/pop-Up Window

If I “Inspect” a pop-up window/message box on chrome browser (by right clicking a web-page in chrome browser) there is a field called “Accessibility”.

Under “Accessibility”, there are “GenericContainer” which has “list”. this list has a number of names as values (e.g. different type of pen).

I would like to copy all values (names) of “list” and separate each value (names) by “;” when I click that pop-up/ message box using a Add-On in Chrome.

How can I make that Add-On?

I understand that I have to write javascript to execute with other .js file, for example, codes in this tutorial-
https://markb.uk/building-a-simple-google-chrome-extension.html
But I don’t know related function I need to call.

Please keep it in your mind that I am new. Thanks in advance!

PS:

  1. At least provide some tutorial, where I can find related instruction.