%YAML 1.1
%TAG ! tag:stsci.edu:asdf/
--- !core/asdf-1.1.0
wcs: !<tag:stsci.edu:gwcs/wcs-1.0.0>
  name: ''
  steps:

#  First (primary) chain ends with a step that has no transform.
  - !<tag:stsci.edu:gwcs/step-1.0.0>
    frame: !<tag:stsci.edu:gwcs/frame-1.0.0>
      axes_names: [x1]
      axis_physical_types: ['custom:x']
      name: f1
      unit: [!unit/unit-1.0.0 pixel]
    transform: !transform/shift-1.2.0
       offset: 10.0
  - !<tag:stsci.edu:gwcs/step-1.0.0>
    id: "step_xyz"
    frame: !<tag:stsci.edu:gwcs/frame-1.0.0>
      axes_names: [x2]
      axis_physical_types: ['custom:x']
      name: f2
      unit: [!unit/unit-1.0.0 pixel]
    transform: !transform/shift-1.2.0
       offset: -5.0
  - !<tag:stsci.edu:gwcs/step-1.0.0>
    frame: !<tag:stsci.edu:gwcs/frame-1.0.0>
      axes_names: [x3]
      axis_physical_types: ['custom:x']
      name: f3
      unit: [!unit/unit-1.0.0 pixel]

#  Next (secondary) chain starts with a step that has a reference to a
#  previous step instead of a frame, and ends with a step that has no
#  transform.
  - !<tag:stsci.edu:gwcs/step-1.0.0>
    frame: "step_xyz"
    transform: !transform/shift-1.2.0
       offset: 23.0
  - !<tag:stsci.edu:gwcs/step-1.0.0>
    frame: !<tag:stsci.edu:gwcs/frame-1.0.0>
      axes_names: [x4]
      axis_physical_types: ['custom:x']
      name: f4
      unit: [!unit/unit-1.0.0 pixel]

...