In some rules (notably Australian and Modern American) the winning hand may consist of only Honors and/or combinations of one suit (though often a number of exceptions is allowed). This version of Mah Jong is sometimes called cleared-hand game. This restriction makes winning much more difficult and results in rather high scores.
To specify the prohibition of mixed suits:
Note: Four Winds does not prohibit you from collecting or claiming combinations with mixed suits, but you cant go out on such hand. Declaring Out on a hand which does not meet the requirements specified is considered a faulty declaration of Out, and the normal penalties are applied.
Related topics:
Maximum number of Chows
Minimum points or doubles/faan/han
Require Limit/Special hand
Exceptions