Feature summary (what you would like to be able to do and where):
As a mobile user, I would like to be able to easily search for help and community discussions.
As an editor, I would also like to search other namespaces like templates and user pages from within mobile view.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

• On mobile web, if I perform an empty search or visit Special:Search directly, the page is empty. T300451
• On mobile web (with or without AMC enabled), if I type a search string, then choose “Search within pages” in the drop-down, the search results page doesn't have any widgets to refine the search.
• I learned today from T294799 that there is a profile=advanced parameter but I have not found any affordance / access point for this.

Benefits (why should this be implemented?):

• May benefit new users who don't know about namespace prefixes, nor that they can type them in the search box. Hosts at w:en:WP:Teahouse often advise new users to search on Help://someword// as a technique for finding help documentation. Whereas Vector has a “Help” link in the left sidebar under Contribute (which on w:en: links to Help:Contents), Minerva does not have any Help link as far as I can see.
• Avoids having to hand-type the prefix.
• Typing the namespace prefix only searches for titles (or other pages mentioning the page title), it doesn't search for keywords in pages of the namespace. Adding the selectors would permit full-text search outside ns0.
• Allows experienced users to search across multiple namespaces without switching to desktop view.