> In particular, you added OS-specific info

I also deemed this very useful information. The issue is that it is not documented in the man pages and so those values are pulled straight from the source code. We would need to decide whether we keep such information in our docs, which is subject to change without warning.

> Did you exactly copy the tk manual wordings or rewrite in your own words?

All of the text was originally copied from the man pages. I have done a reasonable amount of rewording, reformatting and elaborating.

> Do you intend to contribute what you wrote?

If we conclude a complete doc is the way to go, I would finish documenting the canvas widget, make relevant reformatting changes (such as moving common widget options) and then open a PR.