The file begins with the four-byte magic number 72371524, and then two four-byte offsets to the polygon and thing records, in that order.

Then there follow records of the following format for polygons, until the offset specified for things:

int                     tex_type_id             ; 0 for flat, 1 for tex
int                     vx_order                ; 0 if floor, 1 if ceil, 2 for both
                                                ; planes, 3 for clockwise vertices
char[8]                 tex_name                ; flat or texture name, null-padded
int                     num_vertices            ; number of vertices in polygon
num_vertices many:
        float   x                               ; Vertex co-ordinate.
        float   y                               ; "
        float   z                               ; "
        float   u                               ; Texture domain co-ordinate.
        float   v                               ; "

Finally there are the thing records, thus:

int     type    ; Class of thing
int     angle   ; Anticlockwise angle from 0-359, 0 being +ve x dir
int     x       ; Position
int     y       ; "
int     z       ; "