In case if you want to add your own control for selecting a file from external file system in the pop-up window to be linked with the existing “Link” control of every basic block, you can define “externalFilesLibrary” param during plugin initialization as follows:

  externalFilesLibrary: {
        buttonText: 'YOUR BUTTON NAME',
        open: openLibrary(onFileSelectCallback, onCancelCallback) {
/* Put your logic here.              
Call                  onFileSelectCallback('https://YOUR_STORAGE_FILE_URL')               when user select the file from external library.               Call                  onCancelCallback()              
when user close the library without file selection. */

Please find a code example here to see how it works.

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