Minecraft wiki entry for execute, associated text: Result
Unparseable if the argument is not specified correctly
If test doesn't pass, terminates when this subcommand is not at the end of the subcommands chain; fails when at the end.
When at the end of the subcommands chain, and the command is successful, success value is 1.
For if mode, result value is the number of matching entities.
For unless mode, result value is 1.