This site is an amazing resource for those who are interested in tikz/pgf
.
Sometimes, the official manual is not as clear as it could be and some important piece of information are given here.
So I'd like to list the answers that could complete the manual. The added content to the manual could result in a link to the site, cited as further reading.
I would suggest on answer per answer. Please add the section of the manual where you think the content would fit most.
Obviously, what I'm trying to do here won't be doable if this list is too large to maintain...