local is the most common symbol extension. It means that the variable is local to the cog and is not set in the .jkl in which the cog is listed. This doesn't mean that if you leave out the local, the variable will be global and accessible to all cogs.If a symbol does not have the local extension and is not assigned a value in the cog, the symbol's value can be set in the level's JKL if the cog is listed there. Example:
int integer local
desc is short for description. It is used to comment on a symbol. Example:thing item desc=powerup
mask is used to assign Mask Flags to a symbol. The Mask Flags control which messages from the symbol are received by the cog. The symbol type descriptions explain the effect of Mask Flags on each symbol type. Mask Flags can only be used with objects whose value is passed from the level's JKL. Example:sector sec1 mask=0x4
linkid provides a way to assign an ID to a symbol that can generate messages. This ID can be retrieved in messages sent by the object with GetSenderID(). Example:sector sec1 linkid=1
nolink blocks the messages sent by a symbol from being received by the cog. Example:sector sec1 nolink