block_write

      filename: <string>
      append: <yes/no>

 This command writes the marked block to a file of a specified name. If the
 append flag is yes, the data is appended to the file instead of overwriting
 it.

 The editor attempts to deduce the language of the file from its filename. If
 this fails, it assumes the file is of the same language as the current
 buffer. ie: if you are editing a "C" file and you write a file 'fred.asm',
 the file will be written with assembler reserved comments.

 eg:  block_write "equates.h" no