The width of the line is in TWIPS (1/20th of a pixel).
The f_start_cap_style and f_end_cap_style can be:
Round is the default, the way line caps looked before version 8. No Cap means that nothing is added at the tip of the line. This means the line stops exactly where you say it should end. The Square Cap is like the No Cap, but it has the cap which is about Width / 2.
The f_join_style can be:
Each time a line is multiple segments, each segment join is rendered using this definition. A Round Join is what we had before. A Bevel Join is a straight line between the end edges of each line (rectangle representing a line.) The Miter Join is similar to a Bevel, except that you can control the length between the tips and the closure of the line. When the miter limit factor is large, it continues the edges of the lines and it looks like triangles or squares.
The f_no_hscale and f_no_vscale flags, when set to 1, request that the stroke thickness not be scaled along with the object.
When f_pixel_hinting is set to 1, the SWF Player forces all the anchors to be placed on a pixel (it ignores sub-pixels.) This can be useful to create small objects which you do not want blurry.
The f_no_close can be set to 1 to request that the first and last points be rendered with caps rather than a join even if they are equal (and thus close the shape.)
The f_miter_limit_factor field is defined whenever the join is set to Miter Join (2). The value is unsigned from 0.0 to about 255.0. Note that under 1.0, it has no effect.