Issue #3041918 by heddn, qymanab: Add examples to file_blob plugin

src/Plugin/migrate/process/FileBlob.php

@@ -13,6 +13,60 @@ use Symfony\Component\DependencyInjection\ContainerInterface;
 /**
  * Copy a file from a blob into a file.
  *
+ * The source value is an indexed array of two values:
+ * - The destination URI, e.g. 'public://example.txt'.
+ * - The binary blob data.
+ *
+ * Available configuration keys:
+ * - reuse: true
+ *
+ * Examples:
+ *
+ * @code
+ * uri:
+ *   plugin: file_blob
+ *   source:
+ *     - 'public://example.txt'
+ *     - blob
+ * @endcode
+ *
+ * A basic configuration.
+ *
+ * @code
+ * source:
+ *   constants:
+ *     destination: public://images
+ * process:
+ *   destination_blob:
+ *     plugin: callback
+ *     callable: base64_decode
+ *     source:
+ *       - blob
+ *   destination_basename:
+ *     plugin: callback
+ *     callable: basename
+ *     source: file_name
+ *   destination_path:
+ *     plugin: concat
+ *     source:
+ *       - constants/destination
+ *       - @destination_basename
+ *   uri:
+ *     plugin: file_blob
+ *     source:
+ *       - @destination_path
+ *       - @destination_blob
+ * @endcode
+ *
+ * In some instances, it may be necessary to manipulate values before they can
+ * be processed by this plugin. This is because this plugin takes a binary blob
+ * and saves it as a file. In many cases, as in this example, the data is base64
+ * encoded and should be decoded first. In destination_blob, the incoming data
+ * is decoded from base64 to binary. The destination_path element is
+ * concatenating the base filename with the destination directory set in the
+ * constants to create the final path. The resulting values are then referenced
+ * as the source of the file_blob plugin.
+ *
  * @MigrateProcessPlugin(
  *   id = "file_blob"
  * )