Per title, I searched substring() in the
[url=http://processing.org/reference/index_ext.html]Extended
Reference[/url] page to link to it in a Discourse message, and didn't found it.
I saw later it is listed in the String reference page.
If it is on design (keep the reference page light), OK, although I am not
sure it is a good idea... :-) After all you took the time to make a
specific page instead of just pointing to Sun's page...
If it is just an overlook, perhaps this bug report might be useful... ;-)

substring() isn't alone, length() isn't listed too, etc.

We list all of the methods for classes on their class reference pages. For
example, you get everything inside of String here:
http://www.processing.org/reference/String.html

You can get an idea of how much longer your suggestion would make the
reference index page if you look at these entries:
http://www.processing.org/reference/PShape.html
http://www.processing.org/reference/PImage.html
http://www.processing.org/reference/XMLElement.html
http://www.processing.org/reference/PVector.html

I'll leave this bug report open to see if anyone else would like to express
their opinion.

Well, it makes sense... As long as it is not an overlook... :-)

Indeed, it is not a substring(str, i, j) function, like nfs and friends, it
is a method (and a native one, here). So I wouldn't mind if you closed this
entry.

I see you added some Collection classes too, good idea. And of course, you
cannot list all their methods, even the small useful subset you list.

I'm marking this as "resolved," but I'll keep it in mind. It would nice to
move all method reference entries closer to the surface, but I don't think
it's possible with the current system.