This test only works in WKTR or DRT.
Valid system preview
Result:
Valid system preview (multiple rel values)
Result:
Valid system preview (picture child)
Result:
Invalid system preview (wrong rel value)
Result:
Invalid system preview (wrong children)
hello
Result:
Invalid system preview (too many children)
hello
Result:
Invalid system preview (no children)
Result:
Invalid system preview (just an image)
Result: