is the code for this plugin available anywhere? I want to copy it's path selector features so I can create a custom button plugin.
Using K13 Core
To open a page/path selector from your custom button plugin, you can just call the Kentico's content selector javascript API like so:
window.kentico.modalDialog.contentSelector.open({ tabs: ["page"], applyCallback: (data) => {} })
Check out the documentation for more options https://docs.xperience.io/developing-websites/page-builder-development/selectors-for-page-builder-components/using-content-selector-javascript-api