Below is a list of tasks, categorised by intended audience. There will be overlap so treat this as a rough guide only.
Users are visitors to a Joomla! website; administrators are people who install and maintain the website. The assumption is that these people will not know how to write code.
Web designers are those people tasked with creating a Joomla! website that will later be looked after by an administrator. These people can be assumed to know about HTML and CSS but may have only minimal knowledge of PHP.
By "core developers" we mean developers who are contributing to the Joomla! core distribution which includes the core extensions as well as the Framework.
By "third-party developers" we mean developers who are working on extensions to Joomla! (components, modules, plugins and templates) which are made available separately from the Joomla! distribution.
These people may be testing functionality from a user perspective; or they may be developers testing the code itself.
Stuff that pertains to multiple audiences.
This is meta documentation for use by the Documentation Working Group and other documentors.