A match clause can indicate that a blank character must appear in the input.  A blank is identified by the keyword blank in the match clause.  You can define the exact column position that must be blank, the range of column positions (one of which must contain a blank), or no column positions, so that the presence of a blank anywhere in the input satisfies the match clause.  For example:

 

response to line        col 9 blank from        Prog

 

requires that column position 9 of the input be blank and that the input be terminated with a newline character (\n).

The presence of any non-blank character in this position does not satisfy the match clause.

In the response statement:

 

response to char        col 9 thru 15 blank from        Prog

 

there must be a blank character somewhere within positions 9 through 15 of the input.  The response statement:

response to char blank from        Prog

 

is satisfied if any column position in the input is blank.