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--- &(tag)

Following operators support logical expressions of canvas tags
(for Tk8.3+). If tag1.path is 't1' and tag2.path is 't2', then

     ltag = tag1 & tag2; ltag.path => "(t1)&&(t2)"
     ltag = tag1 | tag2; ltag.path => "(t1)||(t2)"
     ltag = tag1 ^ tag2; ltag.path => "(t1)^(t2)"
     ltag = - tag1;      ltag.path => "!(t1)"

