Specifications

B-9Calculatin Page Width Using Printer Colon File Escape Sequence
returned to the evaluation of wQ. The 4 will cause wQ to be assigned the value of s4 (the
envelope size for manual envelope size, a 3). When the evaluation of wK is resumed, the u
value of 4 will direct the process into the else piece of the outer if–then–else statement, and
the Q value of 3 will select an envelope width of 2498 pels.
• Our example is case 1: neither the O nor the u flags were used on the command line, so
Wu is assigned a value of 1, the default _u value for this colon file. When the evaluation
of wQ resumes, the match occurs on s1, and a 1 is returned to the evaluation of wK.
The u value of 1 direct the process into the if piece of the outer if–then–else statement,
and the Q value of 1 selects a page width of 3200 pels. This value is returned to the
evaluation of _w.
The remaining printer colon file escape sequences defining _w reason that if there are 3200
pels available (horizontally), and if we want 12 characters per inch, and if the resolution of
printer is 300 pels per inch, then 128 characters can be printed across the page. Both the
pitch and the printer resolution are multiplied by 10 to account for the possibility of a
17–pitch being specified. A 17–pitch is actually 17.1, so multiplying both the numerator and
the denominator by 10 causes the .1 to be accounted for in the final calculation of page
width. The value 128 is returned to the evaluation of ia. That’s basically where the –128 in
the PIPELINE OF FILTERS came from.