Shared search
It is possible to group Mosaic sites together into collections, so that multiple sites can be searched simultaneously. For example, research group or research project sites could be added to the search collection for a departmental website, so that visitors searching the departmental site could opt to also see results from the group or project sites.
The Research Showcase site search collection includes the website for T3 For All, a fictional research project. When the main search box (towards the top of the screen) is used, the results will be organised under two tabs, 'This site', and 'Include child sites'. The latter is searching across all the sites in the collection. To see this in action, try searching for "T3 conference": this will return different results depending on which tab is viewed.
The label for the site collection results ('Include child sites' in this case) can be customised as desired.
See the documentation on the main Mosaic service site for full details of how to set up and use different search scopes.
See also the Shared content feature, which allows content created on one site to be displayed on another.
Section search
It's also possible to limit the search function to a particular collection of pages and/or files on a Mosaic site. You can try this out below: this search box, unlike the one towards the top of the screen, will only search within the features gallery.
To use section search on a Mosaic site, you'll need to contact the Mosaic team directly to ask to have this functionality enabled on your site. Full details of how to set up a section search are available in the documentation section of the main Mosaic service site.