[thaumasiotes]

Well, not always; one prominent use of semicolons is as the delimiter of an outer list of inner, comma-delimited lists. They're also used in a similar-but-not-quite-identical way to delimit lists in which the items are extremely long.

    To qualify for [some involved definition], the situation must satisfy:
    
    (1) Blah blah blah blah blah blah blah blah blah, blah blah blah blah, blah blah blah blah. Blah blah blah blah blah, blah blah; AND

    (2) Blah blah blah blah blah, blah blah blah blah blah blah blah blah blah. Blah blah blah blah; AND
    
    (3) either
    
      (a) Blah blah blah blah; OR
      
      (b) Blah blah blah blah blah blah, blah blah, blah blah, blah blah blah blah blah.

This is essentially the same idea as defining an ASCII "record separator": you have data that is difficult to distinguish from ordinary delimiters, so you hope that by using a rare, exotic delimiter, the problem will go away.