$ cat test
foo
a
  bar
b
1 foo 2 bar 3
1 foo2bar 3




bar
a
  foo
b
1 bar 2 foo 3
1 bar2foo 3
$ pcregrep -M '(foo.*(.*\n){0,4}.*?bar)?(bar.*(.*\n){0,4}.*?foo)?' test
foo
a
  bar
b
1 foo 2 bar 3
1 foo2bar 3
bar
a
  foo
b
1 bar 2 foo 3
1 bar2foo