Sets the type of metadata to use. metadata is encoded in json, and each property in the json will become a property of the element itself.

there are three supported types of metadata storage:

attr: inside an attribute. the name parameter indicates *which* attribute.
class: inside the class attribute, wrapped in curly braces: { }
elem: inside a child element (e.g. a script tag). the name parameter
indicates *which* element.
the metadata for an element is loaded the first time the element is accessed via jquery.

as a result, you can define the metadata type, use $(expr) to load the metadata into the elements matched by expr, then redefine the metadata type and run another $(expr) for other elements.