Lojban does not have punctuation marks as such: the denpa bu and the slaka bu are really a part of the alphabet. Other languages, however, use punctuation marks extensively. As yet, Lojban does not have any words for these punctuation marks, but a mechanism exists for devising them: the cmavo ``lau'' of selma'o LAU. ``lau'' must always be followed by a BY word; the interpretation of the BY word is changed from a lerfu to a punctuation mark. Typically, this BY word would be a name or brivla with a ``bu'' suffix.

Why is ``lau'' necessary at all? Why not just use a ``bu''-marked word and announce that it is always to be interpreted as a punctuation mark? Primarily to avoid ambiguity. The ``bu'' mechanism is extremely open-ended, and it is easy for Lojban users to make up ``bu'' words without bothering to explain what they mean. Using the ``lau'' cmavo flags at least the most important of such nonce lerfu words as having a special function: punctuation. (Exactly the same argument applies to the use of ``zai'' to signal an alphabet shift or ``ce'a'' to signal a font shift.)

Since different alphabets require different punctuation marks, the interpretation of a ``lau''-marked lerfu word is affected by the current alphabet shift and the current font shift.