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Global Variables

Focus default_focus Variable
Effectively, the default Focus in Picture::output(). See Picture Reference; Outputting; Functions. It's not really the default, but the version of output() that doesn't take a Focus argument calls another version that does take one, passing default_focus to the latter as its Focus argument.

It's necessary to do this in such a roundabout way, because Picture::output() must be declared before class Focus is completely defined and default_focus is declared.

The declaration Focus& f = default_focus; makes f a reference to default_focus, i.e., it makes f another name for default_focus. This may be convenient, if you don't feel like typing default_focus.