User testimony, search data, and some current wiki behaviors have identified a user need of searching through multiple talk pages at once.
Create a check box named "Discussion" that adds (or removes) the namespaces for Project + all talk namespaces to the list of namespaces being searched.
- when all namespaces associated with the button are included, the checkbox is checked.
- if you click the checkbox in this state, all namespaces associated with this checkbox are removed, the checkbox becomes unchecked
- when some or none (but not all) of the associated namespaces are currently included the checkbox is unchecked
- if you click the checkbox in this state, all namespaces not currently included in the search are included, the checkbox becomes checked.
- when the "all" checkbox is selected, this box is also selected (since the namespaces are also part of all)
Notes: This should be done after T173736 as this sets the setup for this story as well.