Log pen trails

What exactly does the 'log pen vectors' option do? When you hover over it, all it says is 'check to turn on logging pen vectors'.

Once you turn it on, it remembers all the line segments drawn by the pen, and right-clicking on the stage gives a new option "svg" that writes the remembered picture as an svg (vector picture format) file.
Stage (2)

I really think that the text you get when you hover over it should explain what it does more clearly.

Feel free to suggest a concise alternative!

But what you really mean is that I have to get the manual up to date. :~(

Is this good?:
Remember where pen lines start and end for .svg files

Maybe. The trouble is, it assumes you know all about SVGs. Better might be

Capture data for infinitely scalable version of drawn pictures.

Make infinite-precision version of pen traces.

... something like that.

Is there a way to actually add the SVG costume to myCostumes programmatically?
When penTrails is added to myCostumes, it only adds bitmap costumes.

Yes, there is an experimental feature: Once you've dragged an instance of the pen trails block out into the scripting area, you can "relabel" it to pen vectors.

Screen Shot 2020-05-31 at 19.00.40

and then you can use it just like pen trails to get the vector trails. The relabelled block will also save and restore correctly in any projects that use it.