public
DEFAULT = 0
"@type" and "@id"
<?php [ '@type' => 'prefix:Foo', '@id' => 42, ]
COMPACT = 1
"@id" only (identifier type not preserved)
<?php [ '@id' => 'prefix:Foo/42', ]
FRIENDLY = 2
"@type", "@id", "@name" and "@description" (empty values removed)
<?php [ '@type' => 'prefix:Foo', '@id' => 42, '@name' => 'Foo', ]