.fsx files have two parts: the header and the text body. Both primarily consist of ASCII text, with binary formatting codes interspersed (see the FSX Code Reference for a complete listing of all standard codes.)
The Header
The header consists of six lines:
Line 1: The name of the brief (plain ASCII text).
Line 2: The width and height of the page, in inches, separated by commas. (For example, 8.5,11 is standard 8½ x 11 letter paper.)
Line 3: Page margins (left, right, top, bottom), in inches, separated by commas.
Line 4: Stylesheet (repeated for each style: [stylename] #02 [formattingcodes] #01)
Line 5: Character stylesheet (repeated for each style: [stylename] #02 [formattingcodes] #01)
Line 6: The header that should appear at the top of each page (plain ASCII text with binary formatting codes.)
Line 7: The footer that should appear at the bottom of each page (plain ASCII text with binary formatting codes.)
Main Body Text
The rest of the file consists of plain ASCII text interspersed with binary formatting codes (see the FSX Code Reference for a complete listing of all standard codes.) All regular text (including line breaks) that is not part of a formatting code is inserted verbatim into the final document.