function parseSlice( raw, str ) {
	var s = str2slice( str );
	if ( s === null ) {
		throw new Error( format( 'invalid operation. Unsupported slice operation. Value: `%s`.', raw ) );
	}
	return s;
}
Parses a serialized Slice object.

@private
@param {string} raw - original unprocessed input string
@param {string} str - serialized Slice object
@throws {Error} invalid slice operation
@returns {Slice} Slice object

@example
var s = parseSlice( '  Slice(null,null,1)  ', 'Slice(null,null,1)' );
// returns <Slice>