markActiveBufferViews( subtreeJson, bufferViewHeaders ) {

		let header;
		const tileAvailabilityHeader = subtreeJson.tileAvailability;
		// Check for bitstream first, which is part of the current schema.
		// bufferView is the name of the bitstream from an older schema.
		if ( ! isNaN( tileAvailabilityHeader.bitstream ) ) {

			header = bufferViewHeaders[ tileAvailabilityHeader.bitstream ];

		} else if ( ! isNaN( tileAvailabilityHeader.bufferView ) ) {

			header = bufferViewHeaders[ tileAvailabilityHeader.bufferView ];

		}
		if ( header ) {

			header.isActive = true;
			header.bufferHeader.isActive = true;

		}
		const contentAvailabilityHeaders = subtreeJson.contentAvailabilityHeaders;
		for ( let i = 0; i < contentAvailabilityHeaders.length; i ++ ) {

			header = undefined;
			if ( ! isNaN( contentAvailabilityHeaders[ i ].bitstream ) ) {

				header = bufferViewHeaders[ contentAvailabilityHeaders[ i ].bitstream ];

			} else if ( ! isNaN( contentAvailabilityHeaders[ i ].bufferView ) ) {

				header = bufferViewHeaders[ contentAvailabilityHeaders[ i ].bufferView ];

			}
			if ( header ) {

				header.isActive = true;
				header.bufferHeader.isActive = true;

			}

		}
		header = undefined;
		const childSubtreeAvailabilityHeader = subtreeJson.childSubtreeAvailability;
		if ( ! isNaN( childSubtreeAvailabilityHeader.bitstream ) ) {

			header = bufferViewHeaders[ childSubtreeAvailabilityHeader.bitstream ];

		} else if ( ! isNaN( childSubtreeAvailabilityHeader.bufferView ) ) {

			header = bufferViewHeaders[ childSubtreeAvailabilityHeader.bufferView ];

		}
		if ( header ) {

			header.isActive = true;
			header.bufferHeader.isActive = true;

		}

	}
Determine which buffer views need to be loaded into memory. This includes:

<ul>
<li>The tile availability bitstream (if a bitstream is defined)</li>
<li>The content availability bitstream(s) (if a bitstream is defined)</li>
<li>The child subtree availability bitstream (if a bitstream is defined)</li>
</ul>

<p>
This function modifies the buffer view headers' isActive flags in place.
</p>

@param {JSON} subtreeJson The JSON chunk from the subtree
@param {BufferViewHeader[]} bufferViewHeaders The preprocessed buffer view headers
@private