Question about syntax for searching within a group and suggestion for smart groups

I often navigate groups and want to search specifically within those groups.

question: if I click on the group in the sidebar, the following search (⌘F) syntax does not work to find the items in that group containing the term sanford.
scope:selection sanford
What is wrong in the syntax ?

If I use a database smart group to perform the search, it would be nice to include a search window in the database drop down menu. Currently I have to look through hundreds of groups to find the one I am looking for.

thanks very much

This should work in the toolbar search (Cmd-Alt-F) but it does not work in the Search inspector (Cmd-F).

thank you Christian
It still does not work with Cmd-Alt-F
I read the search prefix help.
1- it is not clear in which file types can searches be carried out. Does that include weblok, PDF, etc ?
2- my question is specifically about groups. Does scope: work with groups ? As soon as I type scope:selection the search is empty, irrespective of what I write after

A screenshot might be useful.

I understand now. I have to write text: for the text being searched if I write scope:selection
Sorry for taking your time