What are cropMarks

Hi,

I am trying to figure out what all the arguments to the Canvas object do
and noticed that there is a cropMarks argument. The docstring says the
following:

cropMarks may be True/False or an object with parameters borderWidth,
markColor, markWidth       and markLength

What kind of object can be passed? Are the cropMarks supposed to tell the
developer where the PDF might be cropped when printed? Are they showing the
border of the document?

Thanks,
Mike

-----------------
Mike Driscoll

Blog:   http://blog.pythonlibrary.org
Books: Python 101 <https://gum.co/py101>, Python 201: Intermediate Python
<https://gum.co/py201>