GraphQL Fields API Reference

		register_graphql_field(
			'Document',
			'documentDateFrom',
			[
				'type'        => 'String',
				'description' => __( 'Document validity from', 'wp-graphql' ),
				'resolve'     => function( $post ) {
					$document_date = get_post_meta( $post->ID, 'date_from', true );
					return $document_date;
				},
			]
		);

		$hobbies = [
			'type'        => \WPGraphQL\Types::list_of( \WPGraphQL\Types::string() ),
			'description' => __( 'Custom field for user mutations', 'your-textdomain' ),
			'resolve'     => function( $user ) {
				$hobbies = get_user_meta( $user->userId, 'hobbies', true );
				return ! empty( $hobbies ) ? $hobbies : [];
			},
		];

		register_graphql_field( 'User', 'hobbies', $hobbies );
		register_graphql_field( 'CreateUserInput', 'hobbies', $hobbies );
		register_graphql_field( 'UpdateUserInput', 'hobbies', $hobbies );

@todo: Document that fields on any Type in the Schema are the same, including Root Fields, they're
just fields on the RootQuery Type, so they serve as a root entry into the Schema.