  It is known that if a B\"uchi context-free language (BCFL) consists of
scattered words, then there is an integer $n$, depending only on the language,
such that the Hausdorff rank of each word in the language is bounded by $n$.
Every BCFL is a M\"uller context-free language (MCFL). In the first part of the
paper, we prove that an MCFL of scattered words is a BCFL iff the rank of every
word in the language is bounded by an integer depending only on the language.
  Then we establish operational characterizations of the BCFLs of well-ordered
and scattered words. We prove that a language is a BCFL consisting of
well-ordered words iff it can be generated from the singleton languages
containing the letters of the alphabet by substitution into ordinary
context-free languages and the $\omega$-power operation. We also establish a
corresponding result for BCFLs of scattered words and define expressions
denoting BCFLs of well-ordered and scattered words. In the final part of the
paper we give some applications.
