It allows you to write blocks directly into the save game files used by Half-Life 2 save system when such save is being saved.
Ends current data block started with ISave:StartBlock and returns to the parent block. To avoid all sorts of errors, you must end all blocks you start.
ISave:StartBlock( string name )
Starts a new block of data that you can write to inside current block. Blocks must be ended with ISave:EndBlock.