function onSVG( error ) {
			var msg;
			if ( error ) {
				msg = pos+'   error   '+error.message+'   invalid-equation';
				debug( msg );
				file.message( msg, node );
			} else {
				debug( 'Equation successfully renders.' );
			}
			done();
		}
Callback invoked upon attempting to render a TeX equation.

@private
@param {(Error|null)} error - error object