Question: If a function relies on `$_SESSION['some_var']` then the header comment out to make that clear. How do you do it? Just as text, or what?

Or even `@param`?

Answer: 
You could maybe use [@uses](http://manual.phpdoc.org/HTMLSmartyConverter/PHP/phpDocumentor/tutorial_tags.uses.pkg.html) to document superglobals
**@global** has two usages: to denote a global var's definition, and to highlight a global's usage in a method. This second usage fits your use case.

However, assuming that you are referencing **$\_SESSION['some\_var']** directly in that method, and never denoting it via the "**global**" keyword, it's possible that phpDocumentor's **@global** tag won't *find* it when the method is parsed. As such, **@uses** is probably the best alternative as a means to highlight the method's reliance on that superglobal.

[1] -- <http://manual.phpdoc.org/HTMLSmartyConverter/HandS/phpDocumentor/tutorial_tags.global.pkg.html>