trying to understand the Tor Browser launcher command

In the Tor Browser Launcher Properties the following command is given:

sh -c '"/home/user/Downloads/tor-browser_en-US/Browser/start-tor-browser" --detach || ([ ! -x "/home/user/Downloads/tor-browser_en-US/Browser/start-tor-browser" ] && "$(dirname "$*")"/Browser/start-tor-browser --detach)' dummy %k

I'm guessing that this is for when the /Browser subdirectory is in a nonstandard path/directory location.

Can anyone explain to me how works the clause following the OR ( || operator)? I think this gets used in case /home/user/Downloads/tor-browser_en-US/Browser/start-tor-browser is not possible/not found. But I don't see how this manages to establish the correct alternative path...???

If I type "man sh" it opens manual pages for "dash" rather than "sh" with the -c flag described as:
-c Read commands from the command_string operand instead of from the standard input. Special parameter 0 will be set from the command_name operand and the positional parameters ($1, $2, etc.) set from the remaining argument operands.
I guess the command_string operand is the $PATH/Browser/start-tor-browser
and the remaining argument operands are in this case $1 = "--detach"?

Scanning through the start-tor-browser in an editor I see that the --detach option apparently relates to "Detach from terminal and run Tor Browser in the background."

I can't really see what is meant by "dummy %k".

Please excuse my ignorance and thanks for any suggestions. Although I probably don't need to know all details of how Trisquel works I think its a good idea to try and understand some detail from time to time, as a kind of cross check / sanity check.