getExtensions( shaderStage ) {

		const snippets = [];

		if ( shaderStage === 'vertex' ) {

			const ext = this.renderer.backend.extensions;
			const isBatchedMesh = this.object.isBatchedMesh;

			if ( isBatchedMesh && ext.has( 'WEBGL_multi_draw' ) ) {

				this.enableExtension( 'GL_ANGLE_multi_draw', 'require', shaderStage );

			}

		}

		const extensions = this.extensions[ shaderStage ];

		if ( extensions !== undefined ) {

			for ( const { name, behavior } of extensions.values() ) {

				snippets.push( `#extension ${name} : ${behavior}` );

			}

		}

		return snippets.join( '\n' );

	}
Returns the enabled extensions of the given shader stage as a GLSL string.

@param {string} shaderStage - The shader stage.
@return {string} The GLSL snippet that defines the enabled extensions.