While working at Canonical I worked on many different things such as reporting and resolving bugs, implementing drag and drop of tabs and creating a printing framework which works under confinement.
Drag and drop tabs
This was made of many parts, as described below, to ensure that printing could be done under confinement.
The document would then be received by the ubuntu-printing-app which displays the print dialog, it also provides the notifications and queue dialog.
To configure printers, a panel was added to the ubuntu-system-settings app which allows for add, remove and editing of printer options.
The ubuntu-printing-app and ubuntu-system-settings both used a shared component for interacting with CUPS, this was stored in the ubuntu-ui-extras package.