$doc = (object)array(
  "http://schema.org/name" => "Manu Sporny",
  "http://schema.org/url" => (object)array("@id" => "http://manu.sporny.org/"),
  "http://schema.org/image" => (object)array("@id" => "http://manu.sporny.org/images/manu.png")
);

$context = (object)array(
  "name" => "http://schema.org/name",
  "homepage" => (object)array("@id" => "http://schema.org/url", "@type" => "@id"),
  "image" => (object)array("@id" => "http://schema.org/image", "@type" => "@id")
);

// compact a document according to a particular context
// see: http://json-ld.org/spec/latest/json-ld/#compacted-document-form
$compacted = jsonld_compact($doc, $context);

echo json_encode($compacted, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
/* Output:
{
  "@context": {...},
  "image": "http://manu.sporny.org/images/manu.png",
  "homepage": "http://manu.sporny.org/",
  "name": "Manu Sporny"
}
*/

// compact using URLs
jsonld_compact('http://example.org/doc', 'http://example.org/context');

// expand a document, removing its context
// see: http://json-ld.org/spec/latest/json-ld/#expanded-document-form
$expanded = jsonld_expand($compacted) {
echo json_encode($expanded, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES);
/* Output:
{
  "http://schema.org/image": [{"@id": "http://manu.sporny.org/images/manu.png"}],
  "http://schema.org/name": [{"@value": "Manu Sporny"}],
  "http://schema.org/url": [{"@id": "http://manu.sporny.org/"}]
}
*/

// expand using URLs
jsonld_expand('http://example.org/doc');

// flatten a document
// see: http://json-ld.org/spec/latest/json-ld/#flattened-document-form
$flattened = jsonld_flatten($doc);
// all deep-level trees flattened to the top-level

// frame a document
// see: http://json-ld.org/spec/latest/json-ld-framing/#introduction
$framed = jsonld_frame($doc, $frame);
// document transformed into a particular tree structure per the given frame

// normalize a document using the RDF Dataset Normalization Algorithm
// (URDNA2015), see: http://json-ld.github.io/normalization/spec/
$normalized = jsonld_normalize(
  $doc, array('algorithm' => 'URDNA2015', 'format' => 'application/nquads'));
// normalized is a string that is a canonical representation of the document
// that can be used for hashing, comparison, etc.

// force HTTPS-only context loading:
// use built-in secure document loader
jsonld_set_document_loader('jsonld_default_secure_document_loader');

// set a default custom document loader
jsonld_set_document_loader('my_custom_doc_loader');

// a custom loader that demonstrates using a simple in-memory mock for
// certain contexts before falling back to the default loader
// note: if you want to set this loader as the new default, you'll need to
// store the previous default in another variable first and access that inside
// the loader
global $mocks;
$mocks = array('http://example.com/mycontext' => (object)array(
  'hombre' => 'http://schema.org/name'));
function mock_load($url) {
  global $jsonld_default_load_document, $mocks;
  if(isset($mocks[$url])) {
    // return a "RemoteDocument", it has these three properties:
    return (object)array(
      'contextUrl' => null,
      'document' => $mocks[$url],
      'documentUrl' => $url);
  }
  // use default loader
  return call_user_func($jsonld_default_load_document, $url);
}

// use the mock loader for just this call, witout modifying the default one
$compacted = jsonld_compact($foo, 'http://example.com/mycontext', array(
  'documentLoader' => 'mock_load'));

// a custom loader that uses a simplistic in-memory cache (no invalidation)
global $cache;
$cache = array();
function cache_load($url) {
  global $jsonld_default_load_document, $cache;
  if(isset($cache[$url])) {
    return $cache[$url];
  }
  // use default loader
  $doc = call_user_func($jsonld_default_load_document, $url);
  $cache[$url] = $doc;
  return $doc;
}

// use the cache loader for just this call, witout modifying the default one
$compacted = jsonld_compact($foo, 'http://schema.org', array(
  'documentLoader' => 'cache_load'));