Scope selector

Every rule you create in uMatrix applies to a specific scope. The scope tells uMatrix where a rule should be enforced. For example, you may want to block all network requests to facebook.com everywhere by default (* facebook.com * block), except when visiting web pages from facebook.com (facebook.com facebook.com * allow)

The matrix UI in the popup panel allows you to easily select the scope from which to visualize/create/remove rules, the top-left cell is the scope selector:

It is of course advised that you create rules which apply only for a specific scope, but of course it's convenient that some rules are created in the global scope such that you do not have to constantly create the same rules for many sites. For most it's convenient to create allow rules in the global scope for domains which use is widespread.

For example, although you could keep blocking frame everywhere to keep blocking embedded Youtube videos on various web sites, you may want to create global youtube.com rules in order to be able to play embedded Youtube videos easily everywhere by simply allowing frame on any given web sites (you could also allow frame for youtube.com everywhere if you wish, your choice.)

Anyway, this is the purpose of the scope selector, to easily switch back and forth between scopes. When you switch to a given scope, the matrix will reflect the rules in effects for that scope, i.e. what would happen if the network requests had been made in the selected scope.