Semicolons have taken on a unique role within the cortex engine. They are used to separate things in the same entry line into separate commands.
For example, say you want to spawn a marine and modelswap it into a zealot. Without it you would need to enter two lines, however with it you can type @spawn marine;@modelswap zealot.
Without semicolons splitting command lines the game would otherwise try to spawn a “marine;@modelswap” however with the semicolon present you can do several commands at once.
If you type something in chat it will also split it into two lines. For example if you type “Hey guys!;Remember to not be troublemakers this game and have fun!” It will output as –
Remember to not be troublemakers this game and have fun!