===== graph1.gml =====
Creator "igraph"
Version 1
graph
[
  directed 1
  AttOne "x"
  AttTwo 3.14
  node
  [
    id 1
    b "2"
    c 5.6
    nan ""
  ]
  node
  [
    id 2
    a 2
    b "asd"
    d -Inf
    nan "foo"
  ]
  node
  [
    id 5
    b ""
    nan ""
  ]
  edge
  [
    source 5
    target 1
    weight -0.45
    label "-0.45"
  ]
  edge
  [
    source 2
    target 5
    label "Tom & Jerry's "friendship""
    num1 Inf
  ]
]
======================

===== graph2.gml =====
Creator "igraph"
Version 1
graph
[
  directed 1
  node
  [
    id 0
    Foo ""
  ]
  node
  [
    id 1
    Foo ""
  ]
  node
  [
    id 2
    Foo "bar & baz"
  ]
]
======================

===== graph3.gml =====
Creator "igraph"
Version 1
graph
[
  directed 0
]
======================