What is the convention/standard/best-practice for the placement of a collapse/expand button/indicator on collapsible content?
I've seen many examples of the placement on the left (left of title in LTR languages).
This seems very common in commercial applications and Open Source toolkits.
I've been told that the "standard" is on the right of the title area.
Is this actually a standard (or even established convention)? Where can I find the documentation on this?
I'm looking for documentation or research that demonstrates one vs. the other. In the absence of documentation, I'd like opinions with some support or evidence.