& merge()
 
  Syntax: merge(<string1>,<string2>,<character>)
 
  This function merges <string1> and <string2>, depending on 
  <character>. If a character in <string1> is the same as <character>, 
  it is replaced by the character in the corresponding position in 
  <string2>. The two strings must be of the same length.
 
  Spaces need to be treated specially. A null character is considered 
  to equal a space, for <character>.
 
  Example:
 
  > say merge(AB--EF,abcdef,-)
  You say, "ABcdEF"
  > say merge(AB[space(2)]EF,abcdef,)
  You say, "ABcdEF"
 
  See Also: splice()